Format link with Markdown, not Asciidoc

Author: MarkEWaite

CONTRIBUTING.md

@@ -57,4 +57,4 @@ $ mvn clean verify
 
 Use the ["Report an issue" page](https://www.jenkins.io/participate/report-issue/redirect/#23136) to submit bug reports.
 Please review [existing issues](https://issues.jenkins.io/issues/?jql=resolution%20is%20EMPTY%20and%20component%3D23136) before submitting a new issue.
-Please use the link:https://www.jenkins.io/participate/report-issue/["How to Report an Issue"] guidelines when reporting issues.
+Please use the ["How to Report an Issue"](https://www.jenkins.io/participate/report-issue/) guidelines when reporting issues.