Update CONTRIBUTING.md

Author: gignupg

CONTRIBUTING.md

@@ -24,6 +24,6 @@ Making changes to the code and testing them:
 At the moment this is just a personal note for myself since I'm the only person who can publish a new version to the Chrome Web Store:
 1. Update the version number in `src/manifest.json`
 2. Remove the root-level `build` folder
-3. `$ NODE_ENV=production npm run build`
+3. `NODE_ENV=production npm run build`
 4. Zip the newly created `build` folder
 5. Upload the zipped `build` folder to the Chrome Web Store