Update Travis config

Author: workgena

.travis.yml

@@ -1,19 +1,21 @@
 sudo: required
+
 language: ruby
+
 addons:
   chrome: stable
 
-before_install: gem install bundler -v 1.17.1
+before_install:
+  - gem uninstall -v '>= 2' -i $(rvm gemdir)@global -ax bundler || true
+  - gem install bundler -v '< 2'
 
 script: bundle exec rspec
 
 env:
   matrix:
     - RAILS=5.1.6 AA=1.1.0
-    - RAILS=5.1.6 AA=1.2.1
-    - RAILS=5.2.1 AA=1.3.1
     - RAILS=5.2.1 AA=1.4.0
 
 rvm:
-  - 2.3
-  - 2.5
+  - 2.4
+  - 2.6

Gemfile

@@ -4,11 +4,11 @@ source 'https://rubygems.org'
 gemspec
 
 group :test do
-  gem 'rails', "#{ENV['RAILS'] || '5.2.1'}"
-  gem 'activeadmin', "#{ENV['AA'] || '1.3.1'}"
+  gem 'rails', "~> #{ENV['RAILS'] || '5.2.1'}"
+  gem 'activeadmin', "~> #{ENV['AA'] || '1.3.1'}"
 
   gem 'rspec-rails'
-  gem 'sqlite3'
+  gem 'sqlite3', '~> 1.3.6'
   gem 'database_cleaner'
   gem 'capybara'
   gem 'selenium-webdriver'