Add ability to unittest puppet 4

Author: hunner

.travis.yml

@@ -14,9 +14,14 @@ 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"
   - rvm: 1.8.7
     env: PUPPET_GEM_VERSION="~> 2.7.0" FACTER_GEM_VERSION="~> 1.6.0"
   - rvm: 1.8.7
     env: PUPPET_GEM_VERSION="~> 2.7.0" FACTER_GEM_VERSION="~> 1.7.0"
+  allow_failures:
+    - rvm: 2.1.6
+      env: PUPPET_GEM_VERSION="~> 4.0" STRICT_VARIABLES="yes"
 notifications:
   email: false