Update SvgTest to allow png format

Author: nicolasbeauvais

tests/Conversions/ImageGenerators/SvgTest.php

@@ -17,5 +17,5 @@
 
     $imageFile = $imageGenerator->convert($media->getPath());
 
-    expect(mime_content_type($imageFile))->toEqual('image/jpeg');
+    expect(mime_content_type($imageFile))->toEqual('image/png');
 })->skipWhenRunningLocally();