.travis.yml in mini_racer-0.1.7 vs .travis.yml in mini_racer-0.1.8

@@ -1,15 +1,18 @@
 language: ruby
 rvm:
-  - 2.0
   - 2.1
   - 2.2
-  - 2.3.1
+  - 2.3.3
+  - 2.4.0
 matrix:
   include:
-    - rvm: 2.2
+    - rvm: 2.4.0
       os: osx
-      osx_image: xcode8
+      osx_image: xcode8.2
+    - rvm: 2.4.0
+      os: osx
+      osx_image: xcode7.3
 dist: trusty
 sudo: true
 before_install:
   - gem install bundler -v 1.12.0
 cache: bundler