[infer][PR] Fix CI

Summary:
The CI script complains because it's trying to build infer with an old version of ocaml, so to remedy this I bumped the ocaml version in CI. It looks like the CI passes with this change, I did some testing on my own fork of infer and got the CI job to pass in Travis.
Pull Request resolved: https://github.com/facebook/infer/pull/1206

Differential Revision: D19158154

Pulled By: jvillard

fbshipit-source-id: 1bc21024b

.travis.yml

@@ -1,7 +1,7 @@
 language: c
 sudo: required
 env:
-  - OCAML_VERSION=4.07.1
+  - OCAML_VERSION=4.08.1
 cache:
   directories:
     - ${HOME}/.opam