Add ability to unittest puppet 4

Author: hunner

.travis.yml

@@ -14,5 +14,10 @@ matrix:
     env: PUPPET_GEM_VERSION="~> 3.0"
   - rvm: 2.1.5
     env: PUPPET_GEM_VERSION="~> 3.0" FUTURE_PARSER="yes"
+  - rvm: 2.1.6
+    env: PUPPET_GEM_VERSION="~> 4.0" STRICT_VARIABLES="yes"
+  allow_failures:
+    - rvm: 2.1.6
+      env: PUPPET_GEM_VERSION="~> 4.0" STRICT_VARIABLES="yes"
 notifications:
   email: false