Terser: Fail logical nullish assignment (??=) support

[fedetango]

Bug report or Feature request?
Bug report

Version (complete output of terser -V or specific git commit)
npm Version 5.3.5

* Complete CLI command or minify() options used *
minify(code, {ecma:2020})

terser input
var a = 50;
a ??= 200;

terser output or error
JS_Parse_Error [SyntaxError]: Unexpected token: operator (=)

Expected result
var a = 50; a ??= 200

The nullish logical assignment operator seems to be not supported.

[fabiosantoscode]

Correct. Logical assignment is still not supported

[fabiosantoscode]

To clarify, it's a work in progress

[fabiosantoscode]

Closed in 5907df8941dcfa4b52dfd588331483923795cd1f. Will be released soon