Default path for .go-version file

[ruflin]

Currently to select a go version defined in a file, the following command is needed: gvm use $(cat .go-version). This might not necessarily work on all OS. It would be convenient to have something similar to nvm use which automatically picks a version on a predefined file name.

I was initially thinking of going with .go-version but as there might be other gvm configs in the future, perhaps .gvm would be better. An inside it could be yaml and something like:

version: 1.11.3