Update README to require Ocaml 4.08 (#378)

Author: ngzhian

interpreter/README.md

@@ -15,7 +15,7 @@ The text format defines modules in S-expression syntax. Moreover, it is generali
 
 ## Building
 
-You'll need OCaml 4.07 or higher. Instructions for installing a recent version of OCaml on multiple platforms are available [here](https://ocaml.org/docs/install.html). On most platforms, the recommended way is through [OPAM](https://ocaml.org/docs/install.html#OPAM).
+You'll need OCaml 4.08 or higher. Instructions for installing a recent version of OCaml on multiple platforms are available [here](https://ocaml.org/docs/install.html). On most platforms, the recommended way is through [OPAM](https://ocaml.org/docs/install.html#OPAM).
 
 Once you have OCaml, simply do