parsing and then unparsing removes =

[naugtur]

I've been trying to get unparsed arguments passed on to npm6 and yargs parser+unparser turns --omit=dev that npm6 understands into ['--omit', 'dev'] which it doesn't.
I know it's not great of npm6 to do that, but it is an issue with unparser that it produces a different set of arguments.

It could use a hint from parser weather the value was given via = or not.

[shadowspawn]

Related: #80