.travis.yml in immutable-struct-2.1.2 vs .travis.yml in immutable-struct-2.2.0

@@ -1,5 +1,7 @@
 language: ruby
+before_install:
+  - gem install bundler
 rvm:
   - 1.9.3
   - 2.0.0
   - 2.1.0
   - 2.2.2