Fix "Invalid version string" Composer exception for dev-master plugins

When using Composer to update plugins with a version constraint of dev-master, Composer errors out with:

[UnexpectedValueException]
Invalid version string "1.1-git"

The "-git" is already handled for the Roundcube version itself earlier in the same function:

        if (preg_match('/define\(.RCMAIL_VERSION.,\s*.([0-9.]+[a-z-]*)?/', $iniset, $m)) {
            $rcubeVersion = $parser->normalize(str_replace('-git', '.999', $m[1]));
        }