update to latest mocha
fix #7

hashable.format() now enables query string parsing if the format ends in
"?", making these equivalent:

hashable.format("widgets/{widget}?")
hashable.format("widgets/{widget}").query(true)

This is most handy in the context of hashable.hash(), which accepts
strings in .format():

hashable.hash()
  .format("widgets/{widget}?")