lens: clear state on %cancel
lens: clear state on %cancel

if you use herb to send a dojo command that doesn't compile,
the lens state doesn't clear and herb no longer works.
this just adds a simple way to clear that state.

ngzax/urbit,ngzax/urbit,ngzax/urbit,urbit/urbit,ngzax/urbit,urbit/urbit,urbit/urbit,ngzax/urbit,urbit/urbit,urbit/urbit,ngzax/urbit,ngzax/urbit,urbit/urbit,urbit/urbit