Negative Lookahead is not a valid Go Regular Expression

[shellscape]

Hey there. Thanks for this plugin.

Using a valid regex: /(\.js(?!on)(x)?)|(\.flow(\..+)?)$/

Esbuild throws the following error:

Build Error: Error: [flow] "onLoad" filter is not a valid Go regular expression: "(\\.js(?<!\\.json)(x)?)|(\\.flow(\\..+)?)$"

While this may not be a bug in the plugin, it's definitely not something I thought I'd run into. I'll report this to esbuild as well, but at the least I think it would be good for the docs to be updated.