Shouldn't the i in fact be an a?

	['آ', 'a'],
	['أ', 'a'],

	['إ', 'i'],

	['ا', 'a'],

You may run the following tests in your shell / Javascript console:

The base / non-accented "a":

["ا", "a"]

node -e "console.log('ا'.codePointAt(0).toString(16)); console.log('ا'.normalize('NFD').replace(/[\u0300-\u036f]/g, '').codePointAt(0).toString(16));"
=>

627
627

First diacritic variant:

["أ", "a"]

node -e "console.log('أ'.codePointAt(0).toString(16)); console.log('أ'.normalize('NFD').replace(/[\u0300-\u036f]/g, '').codePointAt(0).toString(16));"
=>

623
627

Second diacritic variant:

["آ", "a"]

node -e "console.log('آ'.codePointAt(0).toString(16)); console.log('آ'.normalize('NFD').replace(/[\u0300-\u036f]/g, '').codePointAt(0).toString(16));"
=>

622
627

Third diacritic variant:

["إ", "i"]

node -e "console.log('إ'.codePointAt(0).toString(16)); console.log('إ'.normalize('NFD').replace(/[\u0300-\u036f]/g, '').codePointAt(0).toString(16));"
=>

625
627

Why i, when 627 (same as all other variants) which resolves to a when mapped?

https://github.com/sindresorhus/transliterate/blob/master/replacements.js