Test against Ruby 2.1 to 2.4 (#45)

Merge pull request 45

Author: DirtyF

.travis.yml

@@ -8,17 +8,18 @@ branches:
     - master
 
 rvm:
+  - 2.4
+  - 2.3
   - 2.2
   - 2.1
-  - 2.0
 env:
   - ""
   - JEKYLL_VERSION=3.0.0.beta8
   - JEKYLL_VERSION=2.0
 matrix:
   include:
     - # GitHub Pages
-      rvm: 2.1.1
+      rvm: 2.4.0
       env: GH_PAGES=true
     - # Ruby 1.9
       rvm: 1.9