.travis.yml in mini_racer-0.1.15 vs .travis.yml in mini_racer-0.2.0

@@ -1,19 +1,23 @@
 language: ruby
 rvm:
-  - 2.1
-  - 2.2
-  - 2.3.3
-  - 2.4.0
+  - 2.3
+  - 2.4
+  - 2.5
+  - ruby-head
 matrix:
   include:
+    - rvm: 2.5.1
+      os: osx
+      osx_image: xcode9.4
     - rvm: 2.4.0
       os: osx
-      osx_image: xcode8.2
+      osx_image: xcode8.3
     - rvm: 2.4.0
       os: osx
       osx_image: xcode7.3
 dist: trusty
 sudo: true
 before_install:
-  - gem install bundler -v 1.12.0
+  - gem update --system
+  - gem install bundler -v 1.16.2
 cache: bundler