Fix typos in comments [ci skip]

app/helpers/safe_params_helper.rb

 module SafeParamsHelper
-  # Rails 5.0 requires to permit parameters if used in url helpers.
-  # User this helper when generating links with `params.merge(...)`
+  # Rails 5.0 requires to permit `params` if they're used in url helpers.
+  # Use this helper when generating links with `params.merge(...)`
   def safe_params
     if params.respond_to?(:permit!)
       params.except(:host, :port, :protocol).permit!