Repo incompatible with Node 12+

[saxoncameron]

When attempting to run yarn and using Node LTS (~12.13), getting a number of error messages that prevents the installation. Quite a long output, here are the main offenders, it seems:

fsevents

warning Error running install script for optional dependency: "/Users/sacameron/Sites/schematik-forms/node_modules/fsevents: Command failed.

and node-sass

error /Users/sacameron/Sites/schematik-forms/node_modules/node-sass: Command failed.
Exit code: 1
Command: node scripts/build.js
Arguments: 
Directory: /Users/sacameron/Sites/schematik-forms/node_modules/node-sass
Output:
Building: /Users/sacameron/.nvm/versions/node/v12.13.0/bin/node /Users/sacameron/Sites/schematik-forms/node_modules/node-gyp/bin/node-gyp.js rebuild --verbose --libsass_ext= --libsass_cflags= --libsass_ldflags= --libsass_library=
gyp info it worked if it ends with ok

yarn still runs fine when reverting back to node ^11.

[saxoncameron]

FYI above PR is for being explicit with compatible Node version (11) and is separate from a fix to getting Node 12+ support working properly.