travis CHANGE install expect and shunit2 on OS X

To run yanglint tests
diff --git a/.travis.yml b/.travis.yml
index 331b410..d22065e 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -18,6 +18,8 @@
   homebrew:
     packages:
     - cmocka
+    - shunit2
+    - expect
     update: true
 
 jobs: