Catch ENOENT in clear_cache

There's no need for `clear_cache` to fail if the cache doesn't exist,
either because we call `clear_cache` twice or because no cache was
previously written on this particular repo.

bin/git-linguist

@@ -50,6 +50,7 @@ class GitLinguist
 
   def clear_language_stats
     File.unlink(cache_file)
+  rescue Errno::ENOENT
   end
 
   def disable_language_stats