Update .travis.yml

* Update Rubies to latest version.
* Add ruby-head as allow_failures.
  * It's good to know new version Ruby's issue as faster before the release.
  * fast_finish is to get the Travis result as faster
    without waiting the result of the "allow_failures" items.
    See https://blog.travis-ci.com/2013-11-27-fast-finishing-builds/
* Update it because Travis changed the behavior of "bundler install"
  to use --path.
  $ bundle install --path=${BUNDLE_PATH:-vendor/bundle}

.gitignore

@@ -11,6 +11,7 @@ bundle
 .rvmrc
 .vagrant
 Gemfile.lock
+Gemfile.ruby_dep.lock
 spec/.fixtures
 coverage
 .ruby-version

.travis.yml

@@ -3,22 +3,30 @@ bundler_args: --without development
 before_install:
   - gem install bundler
   - gem update bundler
-  - gem install ruby_dep
-  - gem update ruby_dep
+  - bundle install --gemfile=Gemfile.ruby_dep --path vendor/bundle
 rvm:
-  - 2.2.5
+  - 2.2.7
+  - 2.3.4
+  - 2.4.1
+  - ruby-head
   - jruby-head
   - rbx-2
   - jruby-9.1.2.0
 matrix:
   allow_failures:
+    - rvm: ruby-head
     - rvm: jruby-head
     - rvm: rbx-2
   exclude:
+    - rvm: 2.3.4
+      os: osx
+    - rvm: 2.4.1
+      os: osx
     - rvm: jruby-head
       os: osx
     - rvm: rbx-2
       os: osx
+  fast_finish: true
 os:
   - linux
   - osx

Gemfile.ruby_dep

@@ -0,0 +1,3 @@
+source 'https://rubygems.org'
+
+gem 'ruby_dep'