Incorrect result in base36

[GermanJablo]

generateKeyBetween(null, 'a0', '0123456789abcdefghijklmnopqrstuvwxyz') outputs Zz, but 'Z' is not part of the defined alphabet.

For context, here is the thread where I found the error.

[arv]

I agree that this is a bug. The output should only be using the alphabet.

@GermanJablo I don't think it should be too hard to fix in case you want to take a stab at it?

[GermanJablo]

I would love to, but unfortunately I don't have the bandwidth to tackle it. Hopefully someone else can ☺️

[rdsubhas]

Thank you for the great work. I'd like to add that subsequent invocations of this line throws an error: https://github.com/rocicorp/fractional-indexing/blob/main/src/index.js#L215 saying Uncaught Error: a0 >= Zz due to this behavior.