Deprecated Mongo class: Mongo ==> MongoClient

Fixes error: "Deprecated: Blog\DB\DB::connect(): The Mongo class is deprecated, please use the MongoClient class in /Applications/MAMP/htdocs/voterdb/php-mongodb-master/db.php on line 28"
Merge pull request #2 from leegraham/master

Deprecated Mongo class: Mongo ==> MongoClient