[southparkde] Fix naming inconsistency

The class was first called 'SouthparkDe'. It is now changed to
'SouthParkDe' to match the name of the other extractors.

youtube_dl/extractor/__init__.py

@@ -484,7 +484,7 @@ from .soundgasm import (
 from .southpark import (
     SouthParkIE,
     SouthParkEsIE,
-    SouthparkDeIE,
+    SouthParkDeIE,
     SouthParkNlIE
 )
 from .space import SpaceIE

youtube_dl/extractor/southpark.py

@@ -32,7 +32,7 @@ class SouthParkEsIE(SouthParkIE):
     }]
 
 
-class SouthparkDeIE(SouthParkIE):
+class SouthParkDeIE(SouthParkIE):
     IE_NAME = 'southpark.de'
     _VALID_URL = r'https?://(?:www\.)?(?P<url>southpark\.de/(?:clips|alle-episoden)/(?P<id>.+?)(\?|#|$))'
     _FEED_URL = 'http://www.southpark.de/feeds/video-player/mrss/'