Default remote source for Gemfile

I don't know if somebody need this, but I really do. 

Nowadays 99.9% of every Gemfile contains `source 'https://rubygems.org'`.

More than that, if you accidentally delete this line, you'll get a message `add a line like this: ...` in your console. Why can't we add this line automagically? 

Where is `Convention over configuration`? It's the right place for it!