.travis.yml in rib-1.5.4 vs .travis.yml in rib-1.6.0

@@ -1,23 +1,17 @@
 sudo: false
 language: ruby
 
-before_install:
-  - rvm get head
-  - rvm reload
-  - rvm use --install $TRAVIS_RUBY_VERSION --binary --latest
 install: 'gem install bundler; bundle install --retry=3'
-script: 'ruby -r bundler/setup -S rake test'
+before_script: unset CI
+script: 'ruby -vr bundler/setup -S rake test'
 
 matrix:
   include:
-    - rvm: 2.2.5
-    - rvm: 2.3.2
-    - rvm: 2.4.1
+    - rvm: 2.4
+      env: RUBYOPT=--enable-frozen-string-literal
+    - rvm: 2.5
+      env: RUBYOPT=--enable-frozen-string-literal
     - rvm: ruby-head
-    - rvm: jruby-9
+      env: RUBYOPT=--enable-frozen-string-literal
+    - rvm: jruby
       env: JRUBY_OPTS=--debug
-    - rvm: rbx
-
-  allow_failures:
-    - rvm: 2.4.1
-    - rvm: rbx