fix: derive will error when a path does not start with "m/"

[mattgstevens]

Was working through some tests while using this library and noticed that the assert statement for the first section of path was incorrect.

This lead to a closer look and I believe that the only valid first character is m.

Noticed another PR that would have cleared this up but it seems stuck / forgotten https://github.com/cryptocoinjs/hdkey/pull/6.

What do you think @jprichardson @axic ?

[dcousens]

NACK, m is only valid for a master key?

[mattgstevens]

@dcousens ok have updated.

curious to read more about the usage of m', M and M'

when reading through the BIP32 and related I don't see a reference to this.

[dcousens]

@mattgstevens never seen it either, but as @RyanZim pointed out, it could break someones code otherwise.

[mattgstevens]

@dcousens understood.

if / when this library goes to the next major version this would be a good change to include IMO.

[mattgstevens]

@dcousens is there any further changes you would like? otherwise I think this is ready for a merge.

[RyanZim]

@dcousens I'm of the opinion that we should make the change of requiring m only, and just release a major release.

[dcousens]

@RyanZim go for it :+1: - but what about the 12,970 weekly downloads that might appreciate this patch?

[RyanZim]

Well, they can upgrade if they want, otherwise semver to the rescue. While we're at it, could drop old Node versions, currently supports 0.10+

[RyanZim]

Just realized this is in 0.x; should we release v1 since it's basically stable?

[jprichardson]

Yep, good idea to release a 1.0.