Test on ruby 2.4.0-preview2

Koichi Tanaka · Koichi Tanaka · commit 2c1ede554d45 · 2016-09-14T12:09:54.000+09:00
diff --git a/.travis.yml b/.travis.yml
@@ -5,3 +5,4 @@ rvm:
   - 2.2
   - 2.3.0
   - 2.4.0-preview1
+  - 2.4.0-preview2
