Update Configuration.php (#32)

Change scalarPrototype method to be compatible on Symfony < 3.3

Author: ymezard

DependencyInjection/Configuration.php

@@ -94,7 +94,7 @@ public function getConfigTreeBuilder()
                             ->booleanNode('singleTransaction')->end()
                             ->booleanNode('ssl')->end()
                             ->arrayNode('ignoreTables')
-                                ->scalarPrototype()->end()
+                                 ->prototype('scalar')->end()
                             ->end()
                         ->end()
                     ->end()