doc: improve PR-review paragraph in CONTRIBUTING.md

* Remove redundant "blocking it or stopping it" as blocking and stopping
  are the same thing in this case.
* Make another sentence less wordy. Fix incorrect verb conjugation.
  Break into two clear sentences.

PR-URL: #17931
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Jon Moss <me@jonathanmoss.me>
Reviewed-By: Joyee Cheung <joyeec9h3@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Ruben Bridgewater <ruben@bridgewater.de>
Reviewed-By: Gireesh Punathil <gpunathi@in.ibm.com>

Author: Trott

CONTRIBUTING.md

@@ -602,12 +602,11 @@ your name on it. Congratulations and thanks for your contribution!
 All Node.js contributors who choose to review and provide feedback on Pull
 Requests have a responsibility to both the project and the individual making the
 contribution. Reviews and feedback must be helpful, insightful, and geared
-towards improving the contribution as opposed to simply blocking it or
-stopping it. If there are reasons why you feel the PR should not land, explain
-what those are. Do not expect to be able to block a Pull Request from advancing
-simply because you say "No" without giving an explanation. It is also important
-to be open to having your mind changed, and to being open to working with the
-contributor to make the Pull Request better.
+towards improving the contribution as opposed to simply blocking it. If there
+are reasons why you feel the PR should not land, explain what those are. Do not
+expect to be able to block a Pull Request from advancing simply because you say
+"No" without giving an explanation. Be open to having your mind changed. Be open
+to working with the contributor to make the Pull Request better.
 
 Reviews that are dismissive or disrespectful of the contributor or any other
 reviewers are strictly counter to the [Code of Conduct][].