updated gemfile to lastest mcwrapper version
added TODO comment about executable name
can now restore when minecraft is running

was calling old `stop_server` function. changed to `stop_minecraft`.

part of #29
fixing world restoration paths

turns out that after the backup refactor, I didn't fix restoration to
restore from the world subdirectory.
dont' exit in backup_world if doing a restore

this prevents the restore from failing only because backups are
currently disabled.
make sure that backed up data is called 'world'

rather than whatever it's currently set to. this keeps shit predictable
when doing restores.
version bump to 1.6.3