Fix multi OS dependency installation

We could possibly use the master of Universal Ctags for MacOS but that
would introduce another error surface.

Author: janEbert

.travis.yml

@@ -9,11 +9,10 @@ julia:
   - 1.2
   - nightly
 before_install:
-  - sudo apt-get install -y ctags || sudo apt-get install -y universal-ctags || sudo apt-get install -y exuberant-ctags
-addons:
-  homebrew:
-    packages:
-      - ctags
+  - if [ $TRAVIS_OS_NAME = linux ]; then sudo apt-get install -y universal-ctags || sudo apt-get install -y exuberant-ctags || sudo apt-get install -y ctags; fi
+  # If we want the Universal Ctags master. No tagged releases yet.
+  # - if [ $TRAVIS_OS_NAME = osx ]; then brew tap universal-ctags/universal-ctags && brew install --HEAD universal-ctags; fi
+  - if [ $TRAVIS_OS_NAME = osx ]; then brew install ctags; fi
 matrix:
   allow_failures:
     - julia: nightly