Provide source for sp.js

Hi,
Apparently, there's no "source" for sp.js but just a generated file at vendor/assets/javascripts/snowplow/sp.js.
Would it make sense to add it as a node module instead of having it in vendor/?

Without the source, it's difficult to maintain GitLab in Debian.
See the Debian bug report at: https://bugs.debian.org/943987

To fix the same, could you please provide the source?