Add ruby 2.3.1 in Travis-CI testing (rspec#1739)

Author: SweeD

.travis.yml

@@ -34,6 +34,7 @@ script: "script/run_build 2>&1"
 rvm:
   - 1.8.7
   - 2.3.0
+  - 2.3.1
   - 2.2
   - 2.1
   - 2.0.0
@@ -63,6 +64,10 @@ matrix:
       env: RAILS_VERSION=master
     - rvm: 2.3.0
       env: RAILS_VERSION=5.0.0
+    - rvm: 2.3.1
+      env: RAILS_VERSION=master
+    - rvm: 2.3.1
+      env: RAILS_VERSION=5.0.0
   exclude:
     # 3.0.x is not supported on MRI 2.0+
     - rvm: 2.0.0
@@ -73,6 +78,8 @@ matrix:
       env: RAILS_VERSION='~> 3.0.20'
     - rvm: 2.3.0
       env: RAILS_VERSION='~> 3.0.20'
+    - rvm: 2.3.1
+      env: RAILS_VERSION='~> 3.0.20'
     # 4.x is not supported on MRI ruby-1.8.7 or 1.9.2
     - rvm: 1.8.7
       env: RAILS_VERSION='~> 4.0.4'
@@ -103,11 +110,15 @@ matrix:
       env: RAILS_VERSION='~> 3.1.12'
     - rvm: 2.3.0
       env: RAILS_VERSION='~> 3.1.12'
+    - rvm: 2.3.1
+      env: RAILS_VERSION='~> 3.1.12'
   allow_failures:
     - rvm: 2.2.2
       env: RAILS_VERSION=master
     - rvm: 2.3.0
       env: RAILS_VERSION=master
+    - rvm: 2.3.1
+      env: RAILS_VERSION=master
   fast_finish: true
 
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