Fix MacOS ctags installation

Author: janEbert

.travis.yml

@@ -10,6 +10,10 @@ julia:
   - 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
 matrix:
   allow_failures:
     - julia: nightly