Use ssh by default

[AlexDaniel]

$ z bump push

Current branch master is up to date.
Username for 'https://github.com':

Given that the tool is meant to be used by developers, I think it's fair to say that SSH should be used by default when cloning the repos (instead of HTTPS).

[zoffixznet]

That doesn't work for me. I workuse logins and not SSH keys.

This could be handled by a config option tho, potentially asked about when doing z --init