feat: stop using __dirname if APP_ROOT_PATH is defined

[IslamWahid]

• it is not necessary to use __dirname if APP_ROOT_PATH env var is used.
• this should solve a problem when the package is used in an ESM app.

[IslamWahid]

@inxilpro could you please have a look. I've a problem using typeorm which is using your package internally so when I build my app as esm I get an error

Runtime.UnhandledPromiseRejection: ReferenceError: __dirname is not defined in ES module scope
This file is being treated as an ES module because it has a '.js' file extension and

[GoodbyeNJN]

Same issue for me, but return to normal after replacing __dirname.
Suggestion: Is it better to change it like this?

var dirname = '';
try {
    dirname= __dirname
} catch {
    dirname = process.env.APP_ROOT_PATH;
}

var lib = require('./lib/app-root-path.js');
module.exports = lib(dirname);