update bundler version

hsbt · hsbt · commit 17362a8cbc72 · 2017-02-16T14:58:39.000+09:00
diff --git a/.travis.yml b/.travis.yml
@@ -3,4 +3,4 @@ rvm:
   - 2.3.3
   - 2.4.0
   - ruby-head
-before_install: gem install bundler -v 1.11.2
+before_install: gem update bundler
