[cspan] Disable test

It works fine from all my machines, no matter where, but from travis, we get lots of 403s.
Maybe another project is scraping CSPAN from travis and they're blocking the travis machines?

youtube_dl/extractor/cspan.py

@@ -20,6 +20,7 @@ class CSpanIE(InfoExtractor):
             'title': 'Attorney General Eric Holder on Voting Rights Act Decision',
             'description': 'Attorney General Eric Holder spoke to reporters following the Supreme Court decision in [Shelby County v. Holder] in which the court ruled that the preclearance provisions of the Voting Rights Act could not be enforced until Congress established new guidelines for review.',
         },
+        'skip': 'Regularly fails on travis, for unknown reasons',
     }
 
     def _real_extract(self, url):