Ensure we find the correct Regexp::Raw class

[artfuldodger]

With mongoid 5.2.1's addition of the Origin::Extensions::Regexp::Raw module,
the constant lookup was ambiguous.

Here's the exception I was seeing:

NoMethodError:
  undefined method `new' for Origin::Extensions::Regexp::Raw:Module
# /home/rof/cache/bundler/ruby/2.4.0/gems/mongoid-slug-5.3.2/lib/mongoid/slug/unique_slug.rb:133:in `regex_for_slug'

[mongoid-bot]

	1 Warning
⚠️	There’re library changes, but not tests. That’s OK as long as you’re refactoring existing code.

Generated by 🚫 danger

[dblock]

tiny: Maybe add a space above?

[dblock]

Merged thanks, @mzikherman want to cut an update?

[mzikherman]

Yup, will release this as 5.3.3, thanks for fixing @artfuldodger!

[mzikherman]

Released as 5.3.3.