Fix typos and improve the documentation

This is a squash of the following commits, from first to last:

-

Fix minor, random things I’ve come across lately that individually
did not seem worth making a PR for, so I saved them for one commit.

One common error is using “it’s” (which is an abbreviation of “it is”)
when the possessive “its” should be used for indicating possession.

-

Changes include the name of a test, so remove the `[skip ci]` (thanks @senny).

-

Line wrap the changes at 80 chars and add one more doc fix.

-

Add a missing line wrap in the Contributing to Ruby on Rails Guide.

-

Line wrap the `TIP` section in the Contributing to Ruby on Rails Guide as well.

Rendering the guide locally with `bundle exec rake guides:generate` did
not show any change in on-screen formatting after adding the line wrap.

The HTML generated is (extra line added to illustrate where the line
wrap takes place):

    <div class="info"><p>Please squash your commits into a single commit
when appropriate. This

    simplifies future cherry picks and also keeps the git log
clean.</p></div>

-

Squash commits.

1 files changed, 10 insertions, 8 deletions

diff --git a/guides/source/contributing_to_ruby_on_rails.md b/guides/source/contributing_to_ruby_on_rails.md
index 618b6c3799..aeb5bc7f11 100644
--- a/guides/source/contributing_to_ruby_on_rails.md
+++ b/guides/source/contributing_to_ruby_on_rails.md
@@ -374,7 +374,8 @@ A CHANGELOG entry should summarize what was changed and should end with the auth
     *Your Name*
 ```
 
-Your name can be added directly after the last word if you don't provide any code examples or don't need multiple paragraphs. Otherwise, it's best to make as a new paragraph.
+Your name can be added directly after the last word if there are no code
+examples or multiple paragraphs. Otherwise, it's best to make a new paragraph.
 
 ### Updating the Gemfile.lock
 
@@ -406,13 +407,13 @@ Good commit message should be formatted according to the following example:
 Short summary (ideally 50 characters or less)
 
 More detailed description, if necessary. It should be wrapped to 72
-characters. Try to be as descriptive as you can, even if you think that
-the commit content is obvious, it may not be obvious to others. You
-should add such description also if it's already present in bug tracker,
-it should not be necessary to visit a webpage to check the history.
+characters. Try to be as descriptive as you can; even if you think that the
+commit content is obvious, it may not be obvious to others. Add any description
+that is already present in relevant issues - it should not be necessary to visit
+a webpage to check the history.
 
-Description can have multiple paragraphs and you can use code examples
-inside, just indent it with 4 spaces:
+The description section can have multiple paragraphs. Code examples can be
+embedded by indenting them with 4 spaces:
 
     class ArticlesController
       def index
@@ -428,7 +429,8 @@ You can also add bullet points:
   long to fit in 72 characters
 ```
 
-TIP. Please squash your commits into a single commit when appropriate. This simplifies future cherry picks, and also keeps the git log clean.
+TIP. Please squash your commits into a single commit when appropriate. This
+simplifies future cherry picks and also keeps the git log clean.
 
 ### Update Your Branch