ocamlPackages.irmin*: 2.0.0 -> 2.1.0

updated:

* irmin
* irmin-fs
* irmin-git
* irmin-graphql
* irmin-http
* irmin-mem
* irmin-pack (also added new dependecy ocaml_lwt)
* irmin-test
* irmin-unix
* irmin-watcher