Fix Cannot pass parameter by reference in MongoAdapter

[Zeyckler]

I have tried to run my migrations in phpmig using the Mongo PHP Adapter (https://github.com/alcaeus/mongo-php-adapter) because I'm using Doctrine ODM, but when I try to run the migrations the error of Cannot pass parameter 1 by reference appears. With this little fix can work either with the legacy Mongo driver and with the adapter.

This is the error trace:

== 20170830081759 Migration2 migrating
PHP Fatal error:  Cannot pass parameter 1 by reference in /srv/app/vendor/davedevelopment/phpmig/src/Phpmig/Adapter/Mongo.php on line 61
PHP Stack trace:
PHP   1. {main}() /srv/app/vendor/davedevelopment/phpmig/bin/phpmig:0
PHP   2. Symfony\Component\Console\Application->run() /srv/app/vendor/davedevelopment/phpmig/bin/phpmig:30
PHP   3. Symfony\Component\Console\Application->doRun() /srv/app/vendor/symfony/symfony/src/Symfony/Component/Console/Application.php:130
PHP   4. Symfony\Component\Console\Application->doRunCommand() /srv/app/vendor/symfony/symfony/src/Symfony/Component/Console/Application.php:228
PHP   5. Symfony\Component\Console\Command\Command->run() /srv/app/vendor/symfony/symfony/src/Symfony/Component/Console/Application.php:874
PHP   6. Phpmig\Console\Command\MigrateCommand->execute() /srv/app/vendor/symfony/symfony/src/Symfony/Component/Console/Command/Command.php:264
PHP   7. Phpmig\Migration\Migrator->up() /srv/app/vendor/davedevelopment/phpmig/src/Phpmig/Console/Command/MigrateCommand.php:112
PHP   8. Phpmig\Migration\Migrator->run() /srv/app/vendor/davedevelopment/phpmig/src/Phpmig/Migration/Migrator.php:65
PHP   9. Phpmig\Adapter\Mongo->up() /srv/app/vendor/davedevelopment/phpmig/src/Phpmig/Migration/Migrator.php:103

[davedevelopment]

:+1: thank you

[Zeyckler]

Thank you @davedevelopment for the merge. Waiting for the new release :)

[davedevelopment]

Done!