astring 1.8.5 generates invalid code when ?? is used

[znewsham]

Motivation

astring.generate(acorn.parse('const x = (a && a.b) ?? c'))

Expected behavior

In version 1.8.4 the output is

const x = (a && a.b) ?? c;

Actual behavior

In 1.8.5 the (invalid) output is

const x = a && a.b ?? c;

[davidbonnet]

Thanks for reporting this @znewsham.