[channel9] Missing import in __init__

youtube_dl/extractor/__init__.py

@@ -20,6 +20,7 @@ from .brightcove import BrightcoveIE
 from .c56 import C56IE
 from .canalplus import CanalplusIE
 from .canalc2 import Canalc2IE
+from .channel9 import Channel9IE
 from .cinemassacre import CinemassacreIE
 from .clipfish import ClipfishIE
 from .clipsyndicate import ClipsyndicateIE