Fix typo

Author: matthewpwilson

CONTRIBUTING.md

@@ -139,6 +139,6 @@ We have three main branches in our repo:
    - Note: if the only changes being made are to the documentation, do not update the version number.  In this case the GitHub Pages site will be published when `master` is built, but no new version of the plug-in will be published.
 3. Create a release branch locally based on `master`.
 4. Merge commits to be released into the release branch. Avoid cherry-picking changes so that `master` always remains a subset of `dev`.
-5. Make a PR to merge your release brnach into `master`. The reviewer should make sure all commits are suitable to release and version number has been updated appropriately. 
+5. Make a PR to merge your release branch into `master`. The reviewer should make sure all commits are suitable to release and version number has been updated appropriately. 
 6. After the PR is merged, Jenkins will run a build of `master` and publish the new version to registry.npmjs.org.
 7. Delete the release branch.