Update travis test scope

Drop puppet 2.7 testing
Add puppet 3.7.3 testing
Add ruby 2.1.3 testing

Author: Daniel Dreier

.travis.yml

@@ -5,18 +5,21 @@ before_install: rm Gemfile.lock || true
 rvm:
   - 1.9.3
   - 2.0.0
+  - 2.1.3
 script: bundle exec rake test
 env:
-  - PUPPET_VERSION="~> 2.7.0"
   - PUPPET_VERSION="~> 3.1.0"
   - PUPPET_VERSION="~> 3.2.0"
   - PUPPET_VERSION="~> 3.3.0"
   - PUPPET_VERSION="~> 3.4.0"
+  - PUPPET_VERSION="~> 3.7.3"
 matrix:
   exclude:
   - rvm: 2.0.0
-    env: PUPPET_VERSION="~> 2.7.0"
-  - rvm: 2.0.0
     env: PUPPET_VERSION="~> 3.1.0"
-  - rvm: 1.9.3
-    env: PUPPET_VERSION="~> 2.7.0"
+  - rvm: 2.1.3
+    env: PUPPET_VERSION="~> 3.1.0"
+  - rvm: 2.1.3
+    env: PUPPET_VERSION="~> 3.2.0"
+  - rvm: 2.1.3
+    env: PUPPET_VERSION="~> 3.3.0"