dev/launch.sh should ensure the Phabricator assets are built

Created by: lguychard

./dev/launch.sh currently does not ensure the Phabricator assets are built. Which means when trying to use the Phabricator integration with a local dev instance, the Phabricator assets 404:

`sourcegraph.js:13 GET http://127.0.0.1:3080/.assets/extension/scripts/phabricator.bundle.js net::ERR_ABORTED 404 (Not Found)`