Clarify commit message style.

Author: HonkingGoose

book/05-distributed-git/sections/contributing.asc

@@ -59,9 +59,7 @@ The last thing to keep in mind is the commit message.
 Getting in the habit of creating quality commit messages makes using and collaborating with Git a lot easier.
 As a general rule, your messages should start with a single line that's no more than about 50 characters and that describes the changeset concisely, followed by a blank line, followed by a more detailed explanation.
 The Git project requires that the more detailed explanation include your motivation for the change and contrast its implementation with previous behavior -- this is a good guideline to follow.
-It's also a good idea to use the imperative present tense in these messages.
-In other words, use commands.
-Instead of ``I added tests for'' or ``Adding tests for,'' use ``Add tests for.''
+Write your commit message in the imperative: "Fix bug" and not "Fixed bug" or "Fixes bug."
 Here is a https://tbaggery.com/2008/04/19/a-note-about-git-commit-messages.html[template originally written by Tim Pope]:
 
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