Fix #escape to work correctly with non String Objects

Calling FlickRaw with an ActiveSupport::SafeBuffer as a query parameter instead of a regular string breaks the escape function when the string contains special chars (such as " ").

Using $& is harmful in this case because #gsub in SafeBuffer cannot behave like #gsub in String (cf https://www.ruby-forum.com/topic/198458 ).

This is primarily a SafeBuffer issue, but switching to a classical block variable fixes the issue.