Added a lot of Oxford commas

[ci skip] A regular expression was used to find a lot of missing Oxford
commas and add them.  The regular expression was as follows.

", ([a-zA-Z0-9.\`:'\"]+ ){1,6}(or|and) "

1 files changed, 4 insertions, 4 deletions

diff --git a/guides/source/contributing_to_ruby_on_rails.md b/guides/source/contributing_to_ruby_on_rails.md
index 6429fa32c1..ba5d7bbee8 100644
--- a/guides/source/contributing_to_ruby_on_rails.md
+++ b/guides/source/contributing_to_ruby_on_rails.md
@@ -23,7 +23,7 @@ README](https://github.com/rails/rails/blob/master/README.md), everyone interact
 Reporting an Issue
 ------------------
 
-Ruby on Rails uses [GitHub Issue Tracking](https://github.com/rails/rails/issues) to track issues (primarily bugs and contributions of new code). If you've found a bug in Ruby on Rails, this is the place to start. You'll need to create a (free) GitHub account in order to submit an issue, to comment on them or to create pull requests.
+Ruby on Rails uses [GitHub Issue Tracking](https://github.com/rails/rails/issues) to track issues (primarily bugs and contributions of new code). If you've found a bug in Ruby on Rails, this is the place to start. You'll need to create a (free) GitHub account in order to submit an issue, to comment on them, or to create pull requests.
 
 NOTE: Bugs in the most recent released version of Ruby on Rails are likely to get the most attention. Also, the Rails core team is always interested in feedback from those who can take the time to test _edge Rails_ (the code for the version of Rails that is currently under development). Later in this guide, you'll find out how to get edge Rails for testing.
 
@@ -37,7 +37,7 @@ Then, don't get your hopes up! Unless you have a "Code Red, Mission Critical, th
 
 ### Create an Executable Test Case
 
-Having a way to reproduce your issue will be very helpful for others to help confirm, investigate and ultimately fix your issue. You can do this by providing an executable test case. To make this process easier, we have prepared several bug report templates for you to use as a starting point:
+Having a way to reproduce your issue will be very helpful for others to help confirm, investigate, and ultimately fix your issue. You can do this by providing an executable test case. To make this process easier, we have prepared several bug report templates for you to use as a starting point:
 
 * Template for Active Record (models, database) issues: [gem](https://github.com/rails/rails/blob/master/guides/bug_report_templates/active_record_gem.rb) / [master](https://github.com/rails/rails/blob/master/guides/bug_report_templates/active_record_master.rb)
 * Template for testing Active Record (migration) issues: [gem](https://github.com/rails/rails/blob/master/guides/bug_report_templates/active_record_migrations_gem.rb) / [master](https://github.com/rails/rails/blob/master/guides/bug_report_templates/active_record_migrations_master.rb)
@@ -132,7 +132,7 @@ Contributing to the Rails Documentation
 Ruby on Rails has two main sets of documentation: the guides, which help you
 learn about Ruby on Rails, and the API, which serves as a reference.
 
-You can help improve the Rails guides by making them more coherent, consistent or readable, adding missing information, correcting factual errors, fixing typos, or bringing them up to date with the latest edge Rails.
+You can help improve the Rails guides by making them more coherent, consistent, or readable, adding missing information, correcting factual errors, fixing typos, or bringing them up to date with the latest edge Rails.
 
 To do so, make changes to Rails guides source files (located [here](https://github.com/rails/rails/tree/master/guides/source) on GitHub). Then open a pull request to apply your
 changes to master branch.
@@ -384,7 +384,7 @@ $ RUBYOPT=-W0 bundle exec rake test
 
 The CHANGELOG is an important part of every release. It keeps the list of changes for every Rails version.
 
-You should add an entry **to the top** of the CHANGELOG of the framework that you modified if you're adding or removing a feature, committing a bug fix or adding deprecation notices. Refactorings and documentation changes generally should not go to the CHANGELOG.
+You should add an entry **to the top** of the CHANGELOG of the framework that you modified if you're adding or removing a feature, committing a bug fix, or adding deprecation notices. Refactorings and documentation changes generally should not go to the CHANGELOG.
 
 A CHANGELOG entry should summarize what was changed and should end with the author's name. You can use multiple lines if you need more space and you can attach code examples indented with 4 spaces. If a change is related to a specific issue, you should attach the issue's number. Here is an example CHANGELOG entry: