Fix typo in implicit_render

When trying to make a request and the request doesn't have a suitable template, the new error messages are really helpful but there's a small (and I mean, VERY small) typo that has been bugging me for the last few days. This adds the space and restores order to the universe. ❤

actionpack/lib/action_controller/metal/implicit_render.rb

@@ -42,7 +42,7 @@ def default_render(*args)
           "action but none of them were suitable for this request.\n\n" \
           "This usually happens when the client requested an unsupported format " \
           "(e.g. requesting HTML content from a JSON endpoint or vice versa), but " \
-          "it might also be failing due to other constraints, such as locales or" \
+          "it might also be failing due to other constraints, such as locales or " \
           "variants.\n"
 
         if request.formats.any?