Upgrade to latest supported versions of Ruby

.travis.yml

@@ -5,8 +5,8 @@ env:
   - DATABASE_ADAPTER=postgresql
 rvm:
   - 2.4.4
-  - 2.5.1
-  - 2.6.0
+  - 2.5.4
+  - 2.6.2
 gemfile:
   - gemfiles/rails_4_2.gemfile
   - gemfiles/rails_5_0.gemfile
@@ -14,7 +14,7 @@ gemfile:
   - gemfiles/rails_5_2.gemfile
 matrix:
   exclude:
-    - rvm: 2.6.0
+    - rvm: 2.6.2
       gemfile: gemfiles/rails_4_2.gemfile
 cache: bundler
 # Source: <https://docs.travis-ci.com/user/languages/ruby/#bundler-20>

README.md

@@ -267,11 +267,10 @@ below](#matchers).
 
 ## Compatibility
 
-Shoulda Matchers 4 is tested and supported against Rails 5.x, Rails 4.2, RSpec
-3.x, Minitest 5, Minitest 4, and Ruby 2.3+.
+Shoulda Matchers is tested and supported against Ruby 2.4+, Rails 5.x, Rails
+4.2.x, RSpec 3.x, and Minitest 5.x.
 
-For Rails 4.0/4.1 and Ruby 2.0/2.1/2.2 compatibility, please use
-[shoulda-matchers 3.1.3][v3.1.3].
+For Ruby < 2.4 and Rails < 4.1 compatibility, please use [v3.1.3][v3.1.3].
 
 [v3.1.3]: https://github.com/thoughtbot/shoulda-matchers/releases/tag/v3.1.3