Kana / romaji JS open

Katakana ン loses the syllabic-n apostrophe in Hepburn romanization

Katakana ン loses the syllabic-n apostrophe before vowels and Y

Symptom

Katakana ン before a vowel or Y is romanized without the apostrophe, unlike hiragana ん. シンヨウ becomes SHINYOU (should be SHIN'YOU), so it collides with シニョウ.

Minimal repro

const { fromKana } = require('hepburn')
fromKana('しんよう') // SHIN'YOU
fromKana('シンヨウ') // SHINYOU  <- apostrophe dropped

Fix

Map katakana ン to N' (matching hiragana) and add the ンー long-vowel digraph as N', so N is never a katakana map key and toKatakana still round-trips (PAN to パン).

Fix PR → #hepburn-katakana-n-apostrophe