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.

2 files changed, 3 insertions, 3 deletions

diff --git a/activerecord/test/cases/connection_management_test.rb b/activerecord/test/cases/connection_management_test.rb
index f53c496ecd..bab624b78a 100644
--- a/activerecord/test/cases/connection_management_test.rb
+++ b/activerecord/test/cases/connection_management_test.rb
@@ -110,7 +110,7 @@ module ActiveRecord
         assert ActiveRecord::Base.connection_handler.active_connections?
       end
 
-      test "proxy is polite to it's body and responds to it" do
+      test "proxy is polite to its body and responds to it" do
         body = Class.new(String) { def to_path; "/path"; end }.new
         app = lambda { |_| [200, {}, body] }
         response_body = ConnectionManagement.new(app).call(@env)[2]
diff --git a/activerecord/test/cases/connection_pool_test.rb b/activerecord/test/cases/connection_pool_test.rb
index 8d15a76735..aa50efc979 100644
--- a/activerecord/test/cases/connection_pool_test.rb
+++ b/activerecord/test/cases/connection_pool_test.rb
@@ -204,13 +204,13 @@ module ActiveRecord
       end
 
       # The connection pool is "fair" if threads waiting for
-      # connections receive them the order in which they began
+      # connections receive them in the order in which they began
       # waiting.  This ensures that we don't timeout one HTTP request
       # even while well under capacity in a multi-threaded environment
       # such as a Java servlet container.
       #
       # We don't need strict fairness: if two connections become
-      # available at the same time, it's fine of two threads that were
+      # available at the same time, it's fine if two threads that were
       # waiting acquire the connections out of order.
       #
       # Thus this test prepares waiting threads and then trickles in