audio: Relax matching rules for sbc package on wheezy

Some mirrors escape `+` as `%2b` in the URL, which causes the
regex not to match. Relax the regex so that we do not match the
`+` (that was probably overcautious in the first place).

Fixes #1043.
Merge pull request #1044 from drinkcat/wheezy-sbc-relax-match

audio: Relax matching rules for sbc package on wheezy