Merge pull request #486 from rspec/use-strict-predicates

Return a boolean for Support::Ruby.rbx?/truffleruby?

Author: JonRowe

lib/rspec/support/ruby_features.rb

@@ -33,15 +33,15 @@ def jruby_version
       end
 
       def rbx?
-        defined?(RUBY_ENGINE) && RUBY_ENGINE == 'rbx'
+        !!defined?(RUBY_ENGINE) && RUBY_ENGINE == 'rbx'
       end
 
       def mri?
         !defined?(RUBY_ENGINE) || RUBY_ENGINE == 'ruby'
       end
 
       def truffleruby?
-        defined?(RUBY_ENGINE) && RUBY_ENGINE == 'truffleruby'
+        !!defined?(RUBY_ENGINE) && RUBY_ENGINE == 'truffleruby'
       end
     end