Upgrade bundler and extend travis (#1280)

* Use bundler 2.x
* Run Travis tests with Ruby 2.4 / 2.5 / 2.6

.travis.yml

@@ -1,4 +1,8 @@
 language: ruby
+rvm:
+  - 2.4
+  - 2.5
+  - 2.6
 cache: bundler
 env:
   - DB=postgresql
@@ -10,8 +14,8 @@ before_install:
   - "sudo mv -f ~/chromedriver /usr/local/share/"
   - "sudo chmod +x /usr/local/share/chromedriver"
   - "sudo ln -s /usr/local/share/chromedriver /usr/local/bin/chromedriver"
-  - "gem uninstall -v '>= 2' -i $(rvm gemdir)@global -ax bundler || true"
-  - "gem install bundler -v '< 2'"
+  - "gem update --system"
+  - "gem install bundler"
 before_script:
   - "cp config/application-example.yml config/application.yml"
   - "cp config/database-travis.yml config/database.yml"

Gemfile

@@ -1,10 +1,3 @@
-# Use https only for accessing github
-# https://github.com/bundler/bundler/pull/3447
-git_source(:github) do |repo_name|
-  repo_name = "#{repo_name}/#{repo_name}" unless repo_name.include?("/")
-  "https://github.com/#{repo_name}.git"
-end if Bundler::VERSION < '2'
-
 source 'https://rubygems.org'
 
 # core

Gemfile.lock

@@ -520,4 +520,4 @@ DEPENDENCIES
   whenever (= 0.9.4)
 
 BUNDLED WITH
-   1.17.3
+   2.0.2