mention mongo in tests section of readme.
mention mongo in tests section of readme.

dominionenterprises/mongo-queue-php,daniel-sc/mongo-queue-php,chadicus/mongo-queue-php,chadicus/mongo-queue-php,nubs/mongo-queue-php,nubs/mongo-queue-php,dominionenterprises/mongo-queue-php,daniel-sc/mongo-queue-php