Update ruby versions in Travis config

Author: ignisf

.travis.yml

@@ -1,26 +1,26 @@
 language: ruby
 rvm:
-  - 2.3.2
+  - 2.4.0
+  - 2.3.3
   - 2.2
-  - 2.1
-  - rbx-2.2.7
+  - rbx
 matrix:
   include:
-    - rvm: 2.3.2
+    - rvm: 2.4.0
       os: osx
       osx_image: xcode8.2
-    - rvm: 2.2
+    - rvm: 2.4.0
       os: osx
       osx_image: xcode7.3
-    - rvm: system
+    - rvm: 2.4.0
       os: osx
-      osx_image: xcode7.3
+      osx_image: xcode6.4
     - rvm: system
       os: osx
       osx_image: xcode8.2
-    - rvm: 2.3.2
+    - rvm: system
       os: osx
-      osx_image: xcode6.4
+      osx_image: xcode7.3
     - rvm: system
       os: osx
       osx_image: xcode6.4
@@ -29,17 +29,17 @@ matrix:
     - rvm: 1.9.3
   allow_failures:
     - rvm: 1.9.3
-    - rvm: rbx-2.2.7
-    - os: osx
-      osx_image: xcode6.4
+    - rvm: rbx
   fast_finish: true
-bundler_args: --jobs=1 --retry=3
+bundler_args: --jobs=4 --retry=3
 before_install:
   - if [ "$TRAVIS_OS_NAME" == "linux" ]; then sudo apt-get update; fi
   - if [ "$TRAVIS_OS_NAME" == "linux" ]; then sudo apt-get install git-svn; fi
   - if [ "$TRAVIS_OS_NAME" == "linux" ]; then gem update --system; fi
   - if [ "$TRAVIS_OS_NAME" == "linux" ]; then gem update bundler; fi
-  - if [ "$TRAVIS_OS_NAME" == "osx" ]; then sudo gem install bundler ; fi
+  - if [ "$TRAVIS_OS_NAME" == "osx" -a "$TRAVIS_RUBY_VERSION" == "system" ]; then sudo gem install bundler; fi
+  - if [ "$TRAVIS_OS_NAME" == "osx" -a "$TRAVIS_RUBY_VERSION" != "system" ]; then gem update --system; fi
+  - if [ "$TRAVIS_OS_NAME" == "osx" -a "$TRAVIS_RUBY_VERSION" != "system" ]; then gem update bundler; fi
 script:
   - MAKEFLAGS+=-j8 bundle exec rake checkout compile spec binary --trace
 deploy: