Use a configure block for turning off the js_compressor

I was having problems with some .coffee.erb files being compressed before getting to the requirejs optimizer. This resulted in none of my 'required' scripts being concatenated.

Removing the .erb extension 'solved' the issue, but I need .erb - for build timestamps, etc. 

I spent a fun day and a half, and it turned out that clearing the js_compressor in a configure block works. I'd tried other methods, but Sprockets freezes the Environment if cache_classes == true, which is normal for a deployment.