Better error description on a missing constant/module within another

This active support exception was originally committed 7 years ago (https://github.com/rails/rails/commit/2b37d59976268013b7e518e5af244947f688d315), I believe a typo in the error message made it so far and managed to confuse many (including me) along the way (http://stackoverflow.com/questions/4056894/rails-production-env-object-is-not-missing-constant).

Original error message for this case would come up as something like this:

````
NameError: ParentModule is not missing constant ChildModule!
````

Suggest fix would report as:

````
NameError: 'ParentModule' is missing constant/module 'ChildModule'!
````