Merge pull request #912 from jsoref/contributing-if-exists

Fix contribution issue sentence

CONTRIBUTING.md

@@ -41,7 +41,7 @@ specifically:
 
 - Start with a subject line
 - Contain a body that explains _why_ you're making the change you're making
-- Reference an issue number one exists, closing it if applicable (with text such as
+- Reference an issue number if one exists, closing it if applicable (with text such as
   ["Fixes #245" or "Closes #111"](https://help.github.com/articles/closing-issues-using-keywords/))
 
 Aim for [2 paragraphs in the body](https://www.youtube.com/watch?v=PJjmw9TRB7s).
@@ -67,4 +67,4 @@ interesting to work on:
 - To find issues that we particularly would like contributors to tackle, look for
   [issues with the "help wanted" label](https://github.com/GoogleContainerTools/kaniko/issues?q=is%3Aissue+is%3Aopen+label%3A%22help+wanted%22).
 - Issues that are good for new folks will additionally be marked with
-  ["good first issue"](https://github.com/GoogleContainerTools/kaniko/issues?q=is%3Aissue+is%3Aopen+label%3A%22good+first+issue%22).
+  ["good first issue"](https://github.com/GoogleContainerTools/kaniko/issues?q=is%3Aissue+is%3Aopen+label%3A%22good+first+issue%22).