Omit nomodule attribute value as it's boolean

[shinnn]

Before

const {minify} = require('html-minifier');

minify('<script nomodule="nomodule"></script>', {collapseBooleanAttributes: true});
//=> '<script nomodule="nomodule"></script>'

After

const {minify} = require('html-minifier');

minify('<script nomodule="nomodule"></script>', {collapseBooleanAttributes: true});
//=> '<script nomodule></script>'

---

ref. specification of nomodule attribute: https://html.spec.whatwg.org/multipage/scripting.html#attr-script-nomodule

[shinnn]

Could anyone review this?

[alexlamsl]

Please add a test case (around here) to make sure your change is working as expected.