Revert "added listen to list of known gems"
Revert "added listen to list of known gems"

This reverts commit b131a7206110d8b8f12479139e0d7e7e458056ac.

legallybrown/nanoc,remko/nanoc,hilohiro/nanoc,barraq/nanoc,RubenVerborgh/nanoc,nanoc/nanoc,gjtorikian/nanoc