* tell git to checkout the right branch, rather than cloning and then changing.
* clone with depth 1 under travis, to save time.
* less pushd/popd, which print out confusing text - use `cd` in a subshell
instead. (and just avoid it where possible).
* add some markers to the output to let travis roll it up.
Do `npm install` on js-sdk rather than `npm run build`, which will hopefully
mean that `browserify` gets installed before we try to run it.
The README says we should use `npm install` for the react-sdk too, so let's do
that, and bring the travis and jenkins builds into sync with the README.
lukebarnard