Fixes the #silenced? method when "only" patterns are present

As soon as a path is matched against an "only" regexp, it's
not silenced, so it's silenced if it doesn't match any "only"
regexps.
If fixes the previous logic that was requiring a path to match
all "only" patterns in order to not be silenced, meaning that
it was silenced as soon as it didn't match an "only" regexp
(even if it matched another "only" regexp).
Merge pull request #160 from guard/only-fix

Fixes the #silenced? method when "only" patterns are present