Update ruby version testing matrix

Add ruby 2.7.1 and update patch releases for existing rubies.

.gitignore

@@ -1,4 +1,5 @@
 tmp
+gemfiles/.bundle
 gemfiles/*.lock
 Gemfile.lock
 .ruby-version

.travis.yml

@@ -3,15 +3,15 @@ language: ruby
 cache: bundler
 
 before_install:
-  - "gem update --system 2.7.9"
   - "gem install bundler -v '<2'"
 
 rvm:
   - 2.2.10
   - 2.3.8
-  - 2.4.6
-  - 2.5.5
-  - 2.6.2
+  - 2.4.10
+  - 2.5.8
+  - 2.6.6
+  - 2.7.1
   - ruby-head
 
 gemfile:
@@ -23,17 +23,23 @@ gemfile:
 
 matrix:
   exclude:
+    - rvm: 2.7.1
+      gemfile: gemfiles/rails_5_0.gemfile
+    - rvm: 2.7.1
+      gemfile: gemfiles/rails_5_1.gemfile
+    - rvm: 2.7.1
+      gemfile: gemfiles/rails_5_2.gemfile
     - rvm: 2.2.10
       gemfile: gemfiles/rails_6_0.gemfile
     - rvm: 2.3.8
       gemfile: gemfiles/rails_6_0.gemfile
-    - rvm: 2.4.6
+    - rvm: 2.4.10
       gemfile: gemfiles/rails_6_0.gemfile
     - rvm: 2.2.10
       gemfile: gemfiles/rails_head.gemfile
     - rvm: 2.3.8
       gemfile: gemfiles/rails_head.gemfile
-    - rvm: 2.4.6
+    - rvm: 2.4.10
       gemfile: gemfiles/rails_head.gemfile
   allow_failures:
     - rvm: ruby-head

gemfiles/rails_5_2.gemfile

@@ -2,11 +2,9 @@
 
 source "https://rubygems.org"
 
-git_source(:github) { |repo_name| "https://github.com/#{repo_name}.git" }
-
 gem "rake"
 gem "mocha", require: false
 gem "appraisal"
-gem "rails", "~> 5.2", github: 'rails/rails', branch: '5-2-stable'
+gem "rails", "~> 5.2.0"
 
 gemspec path: "../"