Fix invalid pip argument (#1445)
Fix invalid pip argument (#1445)

It's --upgrade (or -U), not --update

I'm not sure why, but I guess Travis' build cache meant we didn't catch this ahead of time
trailofbits/manticore,trailofbits/manticore,montyly/manticore,montyly/manticore,trailofbits/manticore