docs: add passphrase.js to JS list

[coolaj86]

A modern, WebCrypto-based JS implementation.

No dependencies. No webpack / browserify / etc. Just Works™.

Passes all of https://github.com/trezor/python-mnemonic/blob/master/vectors.json.

Demo at: https://therootcompany.github.io/passphrase.js/

[luke-jr]

@slush0 @prusnak @voisine @ebfull

[murchandamus]

Closing, because the "Other Implementations" section has been removed from BIP39.