`uninitialized constant RuboCop::Cop::Lint::Syntax::MSG`

[mensfeld]

Given gemfile and lock:

# frozen_string_literal: true

source 'https://rubygems.org'

gem 'ducalis'

GEM
  remote: https://rubygems.org/
  specs:
    addressable (2.5.2)
      public_suffix (>= 2.0.2, < 4.0)
    ast (2.4.0)
    ducalis (0.12.0)
      git (~> 1.3, >= 1.3.0)
      octokit (>= 4.7.0)
      regexp-examples (~> 1.3, >= 1.3.2)
      regexp_parser (>= 0.5.0)
      rubocop (>= 0.45.0)https://github.com/negomi/oomerang/blob/master/vendor/bundle/gems/erubis-2.7.0/lib/erubis/helpers/rails_form_helper.rb
    faraday (0.15.4)
      multipart-post (>= 1.2, < 3)
    git (1.5.0)
    jaro_winkler (1.5.2)
    multipart-post (2.0.0)
    octokit (4.14.0)
      sawyer (~> 0.8.0, >= 0.5.3)
    parallel (1.17.0)
    parser (2.6.2.1)
      ast (~> 2.4.0)
    psych (3.1.0)
    public_suffix (3.0.3)
    rainbow (3.0.0)
    regexp-examples (1.4.4)
    regexp_parser (1.4.0)
    rubocop (0.67.2)
      jaro_winkler (~> 1.5.1)
      parallel (~> 1.10)
      parser (>= 2.5, != 2.5.1.1)
      psych (>= 3.1.0)
      rainbow (>= 2.2.2, < 4.0)
      ruby-progressbar (~> 1.7)
      unicode-display_width (>= 1.4.0, < 1.6)
    ruby-progressbar (1.10.0)
    sawyer (0.8.1)
      addressable (>= 2.3.5, < 2.6)
      faraday (~> 0.8, < 1.0)
    unicode-display_width (1.5.0)

PLATFORMS
  ruby

DEPENDENCIES
  ducalis

BUNDLED WITH
   2.0.1

when I run Ducalis on a project I get:

uninitialized constant RuboCop::Cop::Lint::Syntax::MSG
vendor/ruby/2.6.0/gems/rubocop-0.67.2/lib/rubocop/cop/cop.rb:117:in `message'
vendor/ruby/2.6.0/gems/rubocop-0.67.2/lib/rubocop/cop/cop.rb:128:in `add_offense'
vendor/ruby/2.6.0/gems/ducalis-0.12.0/lib/ducalis/patched_rubocop/cop_cast.rb:7:in `add_offense'
vendor/ruby/2.6.0/gems/rubocop-0.67.2/lib/rubocop/cop/lint/syntax.rb:35:in `add_offense_from_diagnostic'
vendor/ruby/2.6.0/gems/rubocop-0.67.2/lib/rubocop/cop/lint/syntax.rb:24:in `block in offenses_from_processed_source'
vendor/ruby/2.6.0/gems/rubocop-0.67.2/lib/rubocop/cop/lint/syntax.rb:23:in `each'
vendor/ruby/2.6.0/gems/rubocop-0.67.2/lib/rubocop/cop/lint/syntax.rb:23:in `offenses_from_processed_source'
vendor/ruby/2.6.0/gems/rubocop-0.67.2/lib/rubocop/cop/team.rb:39:in `inspect_file'
vendor/ruby/2.6.0/gems/rubocop-0.67.2/lib/rubocop/runner.rb:273:in `inspect_file'
vendor/ruby/2.6.0/gems/ducalis-0.12.0/lib/ducalis/patched_rubocop/git_runner.rb:6:in `inspect_file'
vendor/ruby/2.6.0/gems/rubocop-0.67.2/lib/rubocop/runner.rb:220:in `block in do_inspection_loop'
vendor/ruby/2.6.0/gems/rubocop-0.67.2/lib/rubocop/runner.rb:252:in `block in iterate_until_no_changes'
vendor/ruby/2.6.0/gems/rubocop-0.67.2/lib/rubocop/runner.rb:245:in `loop'
vendor/ruby/2.6.0/gems/rubocop-0.67.2/lib/rubocop/runner.rb:245:in `iterate_until_no_changes'
vendor/ruby/2.6.0/gems/rubocop-0.67.2/lib/rubocop/runner.rb:216:in `do_inspection_loop'
vendor/ruby/2.6.0/gems/rubocop-0.67.2/lib/rubocop/runner.rb:119:in `block in file_offenses'
vendor/ruby/2.6.0/gems/rubocop-0.67.2/lib/rubocop/runner.rb:137:in `file_offense_cache'
vendor/ruby/2.6.0/gems/rubocop-0.67.2/lib/rubocop/runner.rb:117:in `file_offenses'
vendor/ruby/2.6.0/gems/rubocop-0.67.2/lib/rubocop/runner.rb:105:in `process_file'
vendor/ruby/2.6.0/gems/rubocop-0.67.2/lib/rubocop/runner.rb:82:in `block in each_inspected_file'
vendor/ruby/2.6.0/gems/rubocop-0.67.2/lib/rubocop/runner.rb:81:in `each'
vendor/ruby/2.6.0/gems/rubocop-0.67.2/lib/rubocop/runner.rb:81:in `reduce'
vendor/ruby/2.6.0/gems/rubocop-0.67.2/lib/rubocop/runner.rb:81:in `each_inspected_file'
vendor/ruby/2.6.0/gems/rubocop-0.67.2/lib/rubocop/runner.rb:73:in `inspect_files'
vendor/ruby/2.6.0/gems/rubocop-0.67.2/lib/rubocop/runner.rb:39:in `run'
vendor/ruby/2.6.0/gems/rubocop-0.67.2/lib/rubocop/cli.rb:174:in `execute_runner'
vendor/ruby/2.6.0/gems/rubocop-0.67.2/lib/rubocop/cli.rb:75:in `execute_runners'
vendor/ruby/2.6.0/gems/rubocop-0.67.2/lib/rubocop/cli.rb:47:in `run'
vendor/ruby/2.6.0/gems/ducalis-0.12.0/bin/ducalis:37:in `block in <top (required)>'
/lib/ruby/2.6.0/benchmark.rb:308:in `realtime'
vendor/ruby/2.6.0/gems/ducalis-0.12.0/bin/ducalis:36:in `<top (required)>'
vendor/ruby/2.6.0/bin/ducalis:23:in `load'
vendor/ruby/2.6.0/bin/ducalis:23:in `<top (required)>'
/lib/ruby/gems/2.6.0/gems/bundler-2.0.1/lib/bundler/cli/exec.rb:74:in `load'
/lib/ruby/gems/2.6.0/gems/bundler-2.0.1/lib/bundler/cli/exec.rb:74:in `kernel_load'
/lib/ruby/gems/2.6.0/gems/bundler-2.0.1/lib/bundler/cli/exec.rb:28:in `run'
/lib/ruby/gems/2.6.0/gems/bundler-2.0.1/lib/bundler/cli.rb:463:in `exec'
/lib/ruby/gems/2.6.0/gems/bundler-2.0.1/lib/bundler/vendor/thor/lib/thor/command.rb:27:in `run'
/lib/ruby/gems/2.6.0/gems/bundler-2.0.1/lib/bundler/vendor/thor/lib/thor/invocation.rb:126:in `invoke_command'
/lib/ruby/gems/2.6.0/gems/bundler-2.0.1/lib/bundler/vendor/thor/lib/thor.rb:387:in `dispatch'
/lib/ruby/gems/2.6.0/gems/bundler-2.0.1/lib/bundler/cli.rb:27:in `dispatch'
/lib/ruby/gems/2.6.0/gems/bundler-2.0.1/lib/bundler/vendor/thor/lib/thor/base.rb:466:in `start'
/lib/ruby/gems/2.6.0/gems/bundler-2.0.1/lib/bundler/cli.rb:18:in `start'
/lib/ruby/gems/2.6.0/gems/bundler-2.0.1/exe/bundle:30:in `block in <top (required)>'
/lib/ruby/gems/2.6.0/gems/bundler-2.0.1/lib/bundler/friendly_errors.rb:124:in `with_friendly_errors'
/lib/ruby/gems/2.6.0/gems/bundler-2.0.1/exe/bundle:22:in `<top (required)>'
/bin/bundle:23:in `load'
/bin/bundle:23:in `<main>'

steps to reproduce:

wget https://github.com/negomi/oomerang/blob/master/vendor/bundle/gems/erubis-2.7.0/lib/erubis/helpers/rails_form_helper.rb
bundle exec ducalis rails_form_helper.rb