Use JsSourceParser as default parser for AstAnalyser class

[madina0801]

Issue #223
It was suspiciously easy, let me know if there are any issues :)

[PierreDemailly]

Thanks for contributing, could you update the type here?

js-x-ray/types/api.d.ts

Line 81 in 7422acb

constructor(parser: SourceParser);

[fraxken]

You can probably write a new test in https://github.com/NodeSecure/js-x-ray/blob/master/test/AstAnalyser.spec.js

If we declare the class without any parser and then use it (it should not throw any error).

[fraxken]

@allcontributors please add @madina0801 for code

[allcontributors]

@fraxken

I've put up a pull request to add @madina0801! 🎉