[TravisCI] install camlp4 on OSX because it is no longer part of ocam…

…l (4.02)

.travis.yml

@@ -32,7 +32,7 @@ before_script:
 install:
   - if [ -z "${TRAVIS_OS_NAME}" ]; then export TRAVIS_OS_NAME=linux; fi; # for our forks that do not have mult-os enabled.
   - if [ "${TRAVIS_OS_NAME}" = "linux" ]; then travis_retry sudo apt-get update -qq; travis_retry sudo apt-get install ocaml zlib1g-dev libgc-dev -qq; fi
-  - if [ "${TRAVIS_OS_NAME}" = "osx" ]; then travis_retry brew update; travis_retry brew install phinze/cask/brew-cask; travis_retry brew install ocaml; fi
+  - if [ "${TRAVIS_OS_NAME}" = "osx" ]; then travis_retry brew update; travis_retry brew install phinze/cask/brew-cask; travis_retry brew install ocaml camlp4; fi
   - if [ "${TRAVIS_OS_NAME}" = "linux" ]; then travis_retry git clone https://github.com/HaxeFoundation/neko.git ~/neko && cd ~/neko && make os=${TRAVIS_OS_NAME} -s && sudo make install -s && cd $TRAVIS_BUILD_DIR; fi
   - if [ "${TRAVIS_OS_NAME}" = "osx" ]; then travis_retry brew install neko --HEAD; fi