fix /bin/sh if incompat

[dzuelke]

'git config --get user.name' returns 'Travis CI', which because unquoted gets interpreted as two operators by if, and breaks:

$ bundle exec hatchet ci:setup
sh: 1: [: Travis: unexpected operator

sh-3.2$ if [ `git config --get user.name` ]; then echo 'already set'; else echo 'not set'; fi
sh: [: David: unary operator expected

much easier is to just use the exit status of --get instead

[schneems]

Thanks!