fix a proof in TreeCrash
fix a proof in TreeCrash

oddly enough, [induction l] in Coq-trunk produces an inductive hypothesis
with the premises ordered differently, even though the context is exactly
the same with Coq-trunk and Coq-v8.5..

mit-pdos/fscq-impl,mit-pdos/fscq-impl,mit-pdos/fscq-impl,mit-pdos/fscq-impl,mit-pdos/fscq-impl