miro: Fix parsing of youtube feeds.

Youtube feeds now don't append a "sig" query string argument anymore, so
all those feeds would fail without this patch. For the latter, a pull
request already exists on upstream at pculture/miro#428, so I guess we
can drop our patch upon release of the next new upstream bugfix release.

Signed-off-by: aszlig <aszlig@redmoonstudios.org>