Bump Ruby version, include 2.4

Author: Bart de Water

.travis.yml

@@ -5,8 +5,9 @@ rvm:
   - 1.9.3
   - 2.0.0
   - 2.1.10
-  - 2.2.5
-  - 2.3.1
+  - 2.2.7
+  - 2.3.4
+  - 2.4.1
   - ruby-head
 gemfile:
   - gemfiles/rails_4.0.gemfile
@@ -18,6 +19,10 @@ gemfile:
 matrix:
   fast_finish: true
   exclude:
+    - rvm: 2.4.1
+      gemfile: gemfiles/rails_4.0.gemfile
+    - rvm: 2.4.1
+      gemfile: gemfiles/rails_4.1.gemfile
     - rvm: 1.9.3
       gemfile: gemfiles/rails_5.0.gemfile
     - rvm: 2.0.0