add puppet 2.7.3 (fixed version) to travis matrix

Author: Joshua Hoblitt

.travis.yml

@@ -5,6 +5,7 @@ rvm:
   - 2.0.0
   - ruby-head
 env:
+  - PUPPET_GEM_VERSION="2.7.3"
   - PUPPET_GEM_VERSION="~> 2.7.1"
   - PUPPET_GEM_VERSION="~> 3.0.0"
   - PUPPET_GEM_VERSION="~> 3.1.0"
@@ -14,6 +15,10 @@ matrix:
   allow_failures:
     - rvm: ruby-head
   exclude:
+    - rvm: 1.9.3
+      env: PUPPET_GEM_VERSION="2.7.3"
+    - rvm: 2.0.0
+      env: PUPPET_GEM_VERSION="2.7.3"
     - rvm: 1.9.3
       env: PUPPET_GEM_VERSION="~> 2.7.1"
     - rvm: 2.0.0
@@ -22,6 +27,8 @@ matrix:
       env: PUPPET_GEM_VERSION="~> 3.0.0"
     - rvm: 2.0.0
       env: PUPPET_GEM_VERSION="~> 3.1.0"
+    - rvm: ruby-head
+      env: PUPPET_GEM_VERSION="2.7.3"
     - rvm: ruby-head
       env: PUPPET_GEM_VERSION="~> 2.7.1"
     - rvm: ruby-head