Fix deployment of branch/commit snapshots

Due to a bug (https://github.com/lepture/node-scp2/issues/21) in the program we are using to ssh snapshots onto streams.spec.whatwg.org, commit and branch snapshots have not been being properly deployed since late October. Fixed this by pinning scp2@0.1.4

Worse, we weren't getting notified of this failure because I was erroneously using Travis CI's `after_success` hook to build and deploy the spec and spec snapshots; if that fails, Travis does not notify you. Fixed by using the `script` hook instead.