The website fails to build with node 6

[kepta]

When I try to run the build command on node v6 it fails to build with the following error:

]Using npm to install Node dependencies
50
[2019-01-25 15:04:53 UTC]npm ERR! code ETARGET
51
[2019-01-25 15:04:53 UTC]npm ERR! notarget No matching version found for sockjs-client@0.0.0-unreleasable
52
[2019-01-25 15:04:53 UTC]npm ERR! notarget In most cases you or one of your dependencies are requesting
53
[2019-01-25 15:04:53 UTC]npm ERR! notarget a package version that doesn't exist.
54
[2019-01-25 15:04:53 UTC]

Note, this is a blocker for us to move this repository to its new home at labs.mapbox.com.