Upgrade CI to Bundler 2.1.3 (#9)

.circleci/config.yml

@@ -8,7 +8,7 @@ executors:
 commands:
   bundle_install:
     steps:
-      - run: gem install bundler -v 2.0.2
+      - run: gem install bundler -v 2.1.3
       - run: bundle install --jobs=4 --retry=3
 
 jobs:

.travis.yml

@@ -11,5 +11,5 @@ rvm:
 - 2.6.5
 - 2.7.0
 - ruby-head
-before_install: gem install bundler -v 2.0.2
+before_install: gem install bundler -v 2.1.3
 script: bundle exec rake test

Rakefile

@@ -20,9 +20,10 @@ end
 
 namespace :bump do
   task :bundler do
-    version = Gemfile.bundler_version
+    version = Gem.latest_version_for("bundler").to_s
     replace_in_file ".circleci/config.yml", /bundler -v (\S+)/ => version
     replace_in_file ".travis.yml", /bundler -v (\S+)/ => version
+    replace_in_file "Gemfile.lock", /^BUNDLED WITH\n\s+([\d\.]+)$/ => version
   end
 
   task :ruby do
@@ -63,20 +64,6 @@ def replace_in_file(path, replacements)
   IO.write(path, contents) if contents != orig_contents
 end
 
-module Gemfile
-  class << self
-    def bundler_version
-      lock_file[/BUNDLED WITH\n   (\S+)$/, 1]
-    end
-
-    private
-
-    def lock_file
-      @_lock_file ||= IO.read("Gemfile.lock")
-    end
-  end
-end
-
 module RubyVersions
   class << self
     def lowest_supported