update readme wasm version constraint

README.md

@@ -46,7 +46,7 @@ make via homebrew, and invoke `gmake` instead of `make`.
 
 **Regarding OCaml:** Install OPAM via your package manager, then:
 
-`$ opam install ppx_deriving_yojson zarith pprint "menhir>=20161115" sedlex process fix "wasm>=1.1.1" visitors ctypes-foreign ctypes`
+`$ opam install ppx_deriving_yojson zarith pprint "menhir>=20161115" sedlex process fix "wasm>=2.0.0" visitors ctypes-foreign ctypes`
 
 Next, make sure you have an up-to-date F\*, and that you ran `make` in the
 `ulib/ml` directory of F\*. The `fstar.exe` executable should be on your PATH