[macgamestore] Add extractor (#2043)

youtube_dl/extractor/__init__.py

@@ -97,6 +97,7 @@ from .kickstarter import KickStarterIE
 from .keek import KeekIE
 from .liveleak import LiveLeakIE
 from .livestream import LivestreamIE, LivestreamOriginalIE
+from .macgamestore import MacGameStoreIE
 from .mdr import MDRIE
 from .metacafe import MetacafeIE
 from .metacritic import MetacriticIE