stringWidth('◼') // 2 in v7, 1 in v5
stringWidth('⚠') // 2 in v7, 1 in v5
stringWidth('✔') // 2 in v7, 1 in v5
(likely not complete list)
seems related to emoji-regex package updates
I guess it is not true that every character considered as emoji due to spec occupies double width. At least at current moment in time.
mathiasbynens/emoji-regex#33