Add 5.1 to the travis.yml

Author: Sam Phippen

.travis.yml

@@ -60,14 +60,20 @@ matrix:
       env: RAILS_VERSION=master
     - rvm: 2.2.2
       env: RAILS_VERSION=5-0-stable
+    - rvm: 2.2.2
+      env: RAILS_VERSION=5.1.0.beta1
     - rvm: 2.3.3
       env: RAILS_VERSION=master
     - rvm: 2.3.3
       env: RAILS_VERSION=5-0-stable
+    - rvm: 2.3.3
+      env: RAILS_VERSION=5.1.0.beta1
     - rvm: 2.4.0
       env: RAILS_VERSION=master
     - rvm: 2.4.0
       env: RAILS_VERSION=5-0-stable
+    - rvm: 2.4.0
+      env: RAILS_VERSION=5.1.0.beta1
   exclude:
     # 3.0.x is not supported on MRI 2.0+
     - rvm: 2.0.0