Fixes mislav#73

Relax version requirements for net-ssh and net-scp

It's common for us to have scp style remote urls that use the '~' at the start of the path, to indicate the home directory of the user used at the start of the url. The conversion of these scp style urls to ssh:// urls breaks the path and adds an initial '/' to the `deploy_to` path, causing git-deploy not to work.

There is no way (that I know of) to preserve these paths when converting to an ssh:// style uri, so we need to detect this situation and 'correct' the url by removing the initial '/' when getting the path

…ausing the builds to fail

rubygems/bundler#3558 (comment)

before_restart.rb would make git print an error message when run in a
Rails project without db/migrate. The error would be printed to stderr
which would result in num_migrations being set to 0 (which is correct).
However, printing the error message when there was no error is
confusing.

This commit introduces a check for the existence of db/migrate. If it
exists then git is called. Otherwise num_migrations is set to 0.

Gem update

Closes mislav#85

Don't display an error when no db/migrate

handle ssh urls that use home relative paths (ie. paths starting with ~)