Removing unneeded requirement for the active_support module.

The `active_support` module [adds a lot of functionality](https://github.com/rails/rails/blob/master/activesupport/lib/active_support.rb#L30) that `Mutations` isn't using.

We're still using `Inflections` and `HashWithIndifferentAccess`, however, but these are targeted dependencies that are required for the basic function of the `Mutations` library.

Also, some line-ending whitespace was cleaned up.