Update package.json

updating to scuttlebutt 5.5 will enable memory management in level-scuttlebutt,
doing so with a slightly open range (~...) will mean I will not have to issue a PR for small scuttlebutt patches!)
If you merge this, I will provide this in the new scuttlebutt service.
Merge pull request #4 from dominictarr/patch-1

Update scuttlebutt@~5.5