Replace shortid with nanoid

[vrizo]

Hi!

Your package looks impressive! I think I've found a way how to improve it a little bit :) Please consider replacing shortid with nanoid. There are no significant changes for users, but there are some critical benefits:

• shortid is not maintained anymore (and issue tracker has many important issues);
• shortid has a problem with a random generator (issue) and ID uniformity (issue). nanoid uses hardware random generator and has special uniformity tests (docs);
• Also, nanoid is 10x times faster than shortid.

What do you think about this, @roccomuso?

Thanks!

[roccomuso]

ok, i might consider the switch..

[roccomuso]

done, thanks. It would be cool if we also manage to make the tests pass on Mac.