Update gemfile for Rails 6 (#66)

Rails 6.0 has already been released.
https://weblog.rubyonrails.org/2019/8/15/Rails-6-0-final-release/

Author: giraffate

.travis.yml

@@ -9,13 +9,13 @@ gemfile:
   - gemfiles/rails_5.0.gemfile
   - gemfiles/rails_5.1.gemfile
   - gemfiles/rails_5.2.gemfile
-  - gemfiles/rails_6.0.0.rc1.gemfile
+  - gemfiles/rails_6.0.gemfile
 matrix:
   exclude:
     - rvm: 2.3
-      gemfile: gemfiles/rails_6.0.0.rc1.gemfile
+      gemfile: gemfiles/rails_6.0.gemfile
     - rvm: 2.4
-      gemfile: gemfiles/rails_6.0.0.rc1.gemfile
+      gemfile: gemfiles/rails_6.0.gemfile
   fast_finish: true
   allow_failures:
     - rvm: ruby-head

Appraisals

@@ -17,9 +17,9 @@ appraise "rails-5.2" do
   gem "activemodel-serializers-xml"
 end
 
-appraise "rails-6.0.0.rc1" do
-  gem "activerecord", "6.0.0.rc1"
-  gem "activemodel", "6.0.0.rc1"
+appraise "rails-6.0" do
+  gem "activerecord", "~> 6.0"
+  gem "activemodel", "~> 6.0"
   gem "activemodel-serializers-xml"
   gem "sqlite3", "~> 1.4"
 end

gemfiles/rails_6.0.0.rc1.gemfile renamed to gemfiles/rails_6.0.gemfile

@@ -2,8 +2,8 @@
 
 source "https://rubygems.org"
 
-gem "activerecord", "6.0.0.rc1"
-gem "activemodel", "6.0.0.rc1"
+gem "activerecord", "~> 6.0"
+gem "activemodel", "~> 6.0"
 gem "activemodel-serializers-xml"
 gem "sqlite3", "~> 1.4"