improve a little log output

Hello Rails Core Team

I’m trying to make a first PR to Rails, and here is my first code change what I want to add to Rails.

It’s pretty simple, but I believe would be useful, since almost every day I’m doing same action - copy-pasting log with unpermitted fields and then adding “:” in front of each attribute name.

So the question is why not to prepare for developers string which they can copy-paste from terminal to editor and save efforts.

Please check PR: