es2015 support for Angular 8, 9

[andzejsw]

So far Thruway is only package in my project, which one needs es5. It would be great if there will be support for es2015, cause now already Angular 9 is out. And for better build times it would be great, if there won't be needed code conversion.

[Chronocento]

+1 I think that supporting es2015 could also help with my issue: I'm trying to use thruway.js with an Ionic 5 app, but even changing to es5 the target in tsconfig.json still leads to the same error as Issue #26