Upgrade bundler to help travis, deprecate ruby 2.2 and test with ruby…

… 2.6

.travis.yml

@@ -1,12 +1,12 @@
 sudo: false
 language: ruby
 rvm:
-  - 2.2
   - 2.3
   - 2.4
   - 2.5
+  - 2.6
   - jruby
 before_install:
-  - gem install bundler -v 1.14.6
+  - gem install bundler -v 2.0.1
   # install client spec from official repository:
   - git clone --depth 5 https://github.com/Unleash/client-specification.git client-specification

unleash-client.gemspec

@@ -26,7 +26,7 @@ Gem::Specification.new do |spec|
 
   spec.add_dependency "murmurhash3", "~> 0.1.6"
 
-  spec.add_development_dependency "bundler", "~> 1.14"
+  spec.add_development_dependency "bundler", "~> 2.0"
   spec.add_development_dependency "rake", "~> 10.0"
   spec.add_development_dependency "rspec", "~> 3.0"
   spec.add_development_dependency "webmock", "~> 3.0"