salt should be a string

[warner]

One suggestion: "salt" is usually a string, not an integer. It should be UTF-8 -encoded into bytes (in a Buffer) before use.

[jedp]

It can now be a string or a buffer.

https://github.com/jedp/srp/blob/master/test/test_srp.js#L9

Although I don't see any other practical value for it, I'm keeping the buffer possibility in order to run the RFC 5054 tests.