We should either add this file to .gitignore because all of our dependencies are part of our build process and we want the latest version and if it breaks it is not catastrophic OR we should check this file in (which should be its own commit).
To complicate things, I've started using yarn rather than npm, which generates yarn.lock instead.
It seems kind of heavy to have two different lock files included, so I guess I'm leaning towards adding both of these files to .gitignore (but I'm open to other opinions).