chapter 9: reword

...to make "issues" and "requests" both plural

you can open up GitHub Issue or Pull Requests
->
you can open up GitHub Issues or Pull Requests
                            ^

Author: zipperer

chapter_09_docker.asciidoc

@@ -61,7 +61,7 @@ and this is a very new draft.
 What that means is that I'd, really, really love feedback from readers.
 Please have a go at following along and let me know what you think!
 I'm [email protected], or you can open up
-https://github.com/hjwp/Book-TDD-Web-Dev-Python/issues[GitHub Issue]
+https://github.com/hjwp/Book-TDD-Web-Dev-Python/issues[GitHub Issues]
 or Pull Requests.
 
 Let me know how you got on, if you get stuck on anything,