Modify limitation on request version

Cherry-picked from 82ad299a5fe893bffbd264f86965ed7a6c4181cf but without
the wrong extras adding.

Signed-off-by: Julien Danjou <julien@danjou.info>

Conflicts:
	tools/pip-requires

Change-Id: I241eb2af55a8f42881476beae7f83ec2fbebdeb7