Auto merge of #6226 - bundler:seg-travis-2-5, r=segiddins

 [Travis] Test against Ruby 2.5

The problem was Ruby 2.5 was released yesterday! So this updates Bundler to test against it on CI, as well as acknowledging 2.6 as a new minor.

.travis.yml

@@ -26,16 +26,17 @@ addons:
       secure: "TrzIv116JLGUxm6PAUskCYrv8KTDguncKROVwbnjVPKTGDAgoDderd8JUdDEXrKoZ9qGLD2TPYKExt9/QDl71E+qHdWnVqWv4HKCUk2P9z/VLKzHuggOUBkCXiJUhjywUieCJhI3N92bfq2EjSBbu2/OFHqWOjLQ+QCooTEBjv8="
 
 rvm:
-  - 2.4.2
-  - 2.3.5
+  - 2.5.0
+  - 2.4.3
+  - 2.3.6
 
 # Rubygems versions MUST be available as rake tasks
 # see Rakefile:125 for the list of possible RGV values
 env:
   # We need to know if changes to rubygems will break bundler on release
   - RGV=master
   # Test the latest rubygems release with all of our supported rubies
-  - RGV=v2.7.1
+  - RGV=v2.7.4
 
 matrix:
   include:
@@ -52,9 +53,9 @@ matrix:
       env: RGV=master
     # 1.x mode (we want to keep stuff passing in 1.x mode for now)
     - rvm: 2.4.2
-      env: RGV=v2.7.1 BUNDLER_SPEC_SUB_VERSION=1.98
+      env: RGV=v2.7.4 BUNDLER_SPEC_SUB_VERSION=1.98
     - rvm: 1.8.7
-      env: RGV=v2.7.1 BUNDLER_SPEC_SUB_VERSION=1.98
+      env: RGV=v2.7.4 BUNDLER_SPEC_SUB_VERSION=1.98
 
   allow_failures:
     - rvm: ruby-head

Rakefile

@@ -147,7 +147,7 @@ begin
       rubyopt = ENV["RUBYOPT"]
       # When editing this list, also edit .travis.yml!
       branches = %w[master]
-      releases = %w[v1.3.6 v1.3.7 v1.4.2 v1.5.3 v1.6.2 v1.7.2 v1.8.29 v2.0.14 v2.1.11 v2.2.5 v2.4.8 v2.5.2 v2.6.8 v2.6.14 v2.7.1]
+      releases = %w[v1.3.6 v1.3.7 v1.4.2 v1.5.3 v1.6.2 v1.7.2 v1.8.29 v2.0.14 v2.1.11 v2.2.5 v2.4.8 v2.5.2 v2.6.8 v2.6.14 v2.7.4]
       (branches + releases).each do |rg|
         desc "Run specs with RubyGems #{rg}"
         RSpec::Core::RakeTask.new(rg) do |t|

lib/bundler/current_ruby.rb

@@ -18,6 +18,7 @@ class CurrentRuby
       2.3
       2.4
       2.5
+      2.6
     ].freeze
 
     KNOWN_MAJOR_VERSIONS = KNOWN_MINOR_VERSIONS.map {|v| v.split(".", 2).first }.uniq.freeze