fixed response_message error

jonmchan · jonmchan · commit b799440de2e5 · 2016-07-06T10:30:54.000-04:00
diff --git a/lib/github_api/error.rb b/lib/github_api/error.rb
@@ -21,7 +21,7 @@ def initialize(message=$!)
       end
 
       def backtrace
-        @response_message ? @response_message.backtrace : super
+        @response_message && @response_message.respond_to?(:backtrace) ? @response_message.backtrace : super
       end
     end # GithubError
   end # Error
