Update CONTRIBUTING.md

Co-authored-by: pwseg <86626706+pwseg@users.noreply.github.com>

Author: cmastr

CONTRIBUTING.md

@@ -77,7 +77,7 @@ Sources pages check if the source is a cloud-app, then include information about
 
 Content with in each `.md` file is markdown. For information about styling, and available extensions, see `_src/utils/formatguide.md` or the live version [here](https://segment.com/docs/utils/formatguide).
 
-## Building a Preview
+## Building a preview
 
 Netlify allows you to build a preview environment on any PR you create in GitHub. This is helpful when you want to send out a review, and the formatting and design are important to those reviewers.