Add --stage 1 to babel cmdline
Add --stage 1 to babel cmdline

So we can use trailing function commas. The trailing comma proposal is actually at stage 3 now and there's a babel 6 plugin for it, which  we should use when we switch back to babel 6.

matrix-org/matrix-react-sdk,aperezdc/matrix-react-sdk,matrix-org/matrix-react-sdk,aperezdc/matrix-react-sdk,matrix-org/matrix-react-sdk,aperezdc/matrix-react-sdk,matrix-org/matrix-react-sdk,matrix-org/matrix-react-sdk,aperezdc/matrix-react-sdk,matrix-org/matrix-react-sdk