Update broccoli-filter to latest.
Update broccoli-filter to latest.

Without this, we get older versions of broccoli-kitchen-sink-helpers
that do not properly handle symlinks.

Same issue as described in
https://github.com/broccolijs/broccoli-filter/pull/16.

timmfin/broccoli-coffee,tsing80/broccoli-coffee,joliss/broccoli-coffee