NoMethodError: undefined method `match' for nil:NilClass

This seems to be happening when there is a trailing ampersand with `couples: true` option.
To reproduce

```
> p = People::NameParser.new(couples: true)
> p.parse "John Doe &"
```

Got

```
NoMethodError: undefined method `match' for nil:NilClass
from /home/vagrant/.rvm/gems/ruby-2.2.0/gems/people-0.2.1/lib/people.rb:307:in `block in get_title'
```

People gem version 0.2.1
Ruby version 2.2.0
