Properly add status_code on exceptions. Fixes #255

src/kemal/common_exception_handler.cr

@@ -22,6 +22,7 @@ module Kemal
       if Kemal.config.error_handlers.has_key?(status_code)
         context.response.content_type = "text/html" unless context.response.headers.has_key?("Content-Type")
         context.response.print Kemal.config.error_handlers[status_code].call(context, exception)
+        context.response.status_code = status_code
         context
       end
     end