Added check for empty migrations/versions array.

If there are no versions and no migrations present, the old code
would throw the warning

    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
Merge pull request #42 from seiffert/master

Fixed Warning in case of no migrations present