Merge pull request redis-store#87 from redis-store/ruby24

Update Travis-CI to test against Ruby 2.4.1

.travis.yml

@@ -5,11 +5,11 @@ gemfile:
   - gemfiles/Gemfile.activesupport-4.x
   - gemfiles/Gemfile.activesupport-5.x
 rvm:
-  - 1.9.3
-  - 2.0.0
-  - 2.1.5
-  - 2.2.4
-  - 2.3.0
+  - 2.0
+  - 2.1
+  - 2.2
+  - 2.3
+  - 2.4
   - ruby-head
   - jruby-head
 services:
@@ -18,13 +18,7 @@ matrix:
   allow_failures:
     - rvm: jruby-head
     - rvm: ruby-head
-    - rvm: 1.9.3
+    - rvm: 2.0
       gemfile: gemfiles/Gemfile.activesupport-5.x
-    - rvm: 2.0.0
-      gemfile: gemfiles/Gemfile.activesupport-5.x
-    - rvm: 2.1.5
-      gemfile: gemfiles/Gemfile.activesupport-5.x
-    - rvm: rbx-19mode
-      gemfile: gemfiles/Gemfile.activesupport-5.x
-    - rvm: jruby-19mode
+    - rvm: 2.1
       gemfile: gemfiles/Gemfile.activesupport-5.x