📝 adding an emoji for upgrading deps

CONTRIBUTING.md

@@ -82,6 +82,7 @@ For more information on how to work with Atom's official packages, see
     * :green_heart: `:green_heart:` when fixing the CI build
     * :white_check_mark: `:white_check_mark:` when adding tests
     * :lock: `:lock:` when dealing with security
+    * :arrow_up: `:arrow_up` when upgrading deps
 
 ## CoffeeScript Styleguide