Merge pull request #136 from meh/patch-1

Fix Grape::Middleware::Formatter#headers

Author: Michael Bleigh

lib/grape/middleware/formatter.rb

@@ -15,7 +15,7 @@ def default_options
       end
 
       def headers
-        env.dup.inject({}){|h,(k,v)| h[k.downcase] = v; h}
+        env.dup.inject({}){|h,(k,v)| h[k.downcase[5..-1]] = v if k.downcase.start_with?('http_'); h}
       end
 
       def before