Add rails master to travis CI, allow failures

Author: mrloop

.travis.yml

@@ -4,6 +4,7 @@ env:
   - "RAILS_VERSION=4.1.0"
   - "RAILS_VERSION=4.2.6"
   - "RAILS_VERSION=5.0.0"
+  - "RAILS_VERSION=master"
 rvm:
   - 2.1
   - 2.2.4
@@ -13,4 +14,6 @@ matrix:
     - rvm: 2.0
       env: "RAILS_VERSION=5.0.0"
     - rvm: 2.1
-      env: "RAILS_VERSION=5.0.0"
+      env: "RAILS_VERSION=5.0.0"
+  allow_failures:
+    - env: "RAILS_VERSION=master"