Add RAILS_MASTER to the travis build matrix

.travis.yml

@@ -1,5 +1,21 @@
 language: ruby
 
+env:
+  global:
+    - DISCOURSE_HOSTNAME=www.example.com
+    - RUBY_GC_MALLOC_LIMIT=50000000
+  matrix:
+    - "RAILS_MASTER=1"
+    - "RAILS_MASTER=0"
+
+matrix:
+  allow_failures:
+    - rvm: 2.0.0
+      env: "RAILS_MASTER=1"
+    - rvm: 2.1
+      env: "RAILS_MASTER=1"
+  fast_finish: true
+
 rvm:
   - 2.0.0
   - 2.1
@@ -11,11 +27,6 @@ sudo: false
 
 cache: bundler
 
-env:
-  global:
-    - DISCOURSE_HOSTNAME=www.example.com
-    - RUBY_GC_MALLOC_LIMIT=50000000
-
 before_install:
   - npm i -g jshint
   - jshint .

Gemfile

@@ -4,7 +4,7 @@ source 'https://rubygems.org'
 
 module ::Kernel
   def rails_master?
-    ENV["RAILS_MASTER"]
+    ENV["RAILS_MASTER"] == '1'
   end
 end