Remove references to internal Doctrine class (#492)

The Configuration class is defined as an internal class by Doctrine. Since we don't need to include an empty configuration instance anyways (Doctrine will just create it if it isn't provided), we can avoid referencing internal classes by just leaving it out.

src/Database/Doctrine.php

@@ -16,7 +16,6 @@
     Imbo\Exception\DatabaseException,
     Imbo\Exception\InvalidArgumentException,
     Imbo\Exception,
-    Doctrine\DBAL\Configuration,
     Doctrine\DBAL\DriverManager,
     Doctrine\DBAL\Connection,
     PDO,
@@ -643,7 +642,7 @@ private function setConnection(Connection $connection) {
      */
     private function getConnection() {
         if ($this->connection === null) {
-            $this->connection = DriverManager::getConnection($this->params, new Configuration());
+            $this->connection = DriverManager::getConnection($this->params);
         }
 
         return $this->connection;