Fixed Warning in case of no migrations present

If there are no versions and no migrations present, the old code would trigger the following warning

    $ bin/phpmig migrate
    PHP Warning:  max(): Array must contain at least one element in /srv/www/vhosts/multiez.dev/vendor/davedevelopment/phpmig/src/Phpmig/Console/Command/MigrateCommand.php on line 76

    Warning: max(): Array must contain at least one element in /srv/www/vhosts/multiez.dev/vendor/davedevelopment/phpmig/src/Phpmig/Console/Command/MigrateCommand.php on line 76

One could argue that the command should throw an exception in such this case. I'm not opinionated about this and I wanted to stay compatible with the way the command reacts on [non-existent migrations](https://github.com/davedevelopment/phpmig/blob/master/src/Phpmig/Console/Command/MigrateCommand.php#L73).