No more default digest in node.js 8

[vkoechli]

When running reStore under node.js 8.4.0, trying to sign up a user returns a 500 error: <<The "digest" argument is required and must not be undefined>>. Supposedly a consequence of nodejs/node#11305. The default used to be sha1, but that is no longer the case.

[lesion]

I've fixed this in my fork with this commit:

lesion@cc065ec

[untitaker]

@lesion if you're going to keep maintaining that fork I would suggest merging the commits from https://github.com/untitaker/morestore as well.

[lesion]

done, thanks for the suggestion.