Enable object override to InitDbFixture during FixturesStore initialization (#88)

Author: PoohOka

Diff for: src/Codeception/Lib/Connector/Yii2/FixturesStore.php

@@ -29,7 +29,9 @@ public function fixtures()
     public function globalFixtures()
     {
         return [
-            InitDbFixture::class
+            'initDbFixture' => [
+                'class' => InitDbFixture::class,
+            ],
         ];
     }
 }