Fix issue of last version of bundler not support for Ruby 2.2.

Author: bugtender

.travis.yml

@@ -6,7 +6,12 @@ rvm:
   - 2.5
   - ruby-head
 before_install:
-  - gem install bundler
+  - if [ ${TRAVIS_RUBY_VERSION} = '2.2' ]; then
+      gem install bundler -v '< 2';
+    else
+      gem update --system;
+      gem install bundler;
+    fi
 script:
   - bundle exec rubocop
   - bundle exec rspec

line-bot-api.gemspec

@@ -20,7 +20,7 @@ Gem::Specification.new do |spec|
   spec.required_ruby_version     = '>= 2.0.0'
 
   spec.add_development_dependency "addressable", "~> 2.3"
-  spec.add_development_dependency "bundler", "~> 1.11"
+  spec.add_development_dependency "bundler", "~> 1.11" if RUBY_VERSION < "2.3"
   spec.add_development_dependency 'rake', "~> 10.4"
   spec.add_development_dependency "rspec", "~> 3.0"
   spec.add_development_dependency "webmock", "~> 1.24"