update mirage-http constraint to latest cohttp
Merge branch 'mirage-1.1.0' of github.com:mirage/opam-repository into mirage-1.1.0

Conflicts:
	packages/mirage-http/mirage-http.1.1.0/opam
Merge branch 'mirage-1.1.0' of github.com:mirage/opam-repository into mirage-1.1.0
switch tcpip to the main mirage repo