[9gag] Allow old .tv domain

There are still references to it in webpage's source

youtube_dl/extractor/ninegag.py

@@ -9,7 +9,7 @@
 
 class NineGagIE(InfoExtractor):
     IE_NAME = '9gag'
-    _VALID_URL = r'https?://(?:www\.)?9gag\.com/tv/p/(?P<id>[a-zA-Z0-9]+)(?:/(?P<display_id>[^?#/]+))?'
+    _VALID_URL = r'https?://(?:www\.)?9gag(?:\.com/tv|\.tv)/p/(?P<id>[a-zA-Z0-9]+)(?:/(?P<display_id>[^?#/]+))?'
 
     _TESTS = [{
         "url": "http://9gag.com/tv/p/Kk2X5/people-are-awesome-2013-is-absolutely-awesome",
@@ -28,6 +28,9 @@ class NineGagIE(InfoExtractor):
     }, {
         'url': 'http://9gag.com/tv/p/KklwM',
         'only_matching': True,
+    }, {
+        'url': 'http://9gag.tv/p/Kk2X5',
+        'only_matching': True,
     }]
     _EXTERNAL_VIDEO_PROVIDER = {
         '1': {