Upgrade to Nativescript 7

Hey,

Nativescript recenlty introcuded some big changes (for example they changed the compiler option from "ES-5" to "ES2017"). It would be great if you could bring the whole project up to date. 

Here's the url with all the instructions: [https://nativescript.org/blog/nativescript-7-for-plugin-authors/](https://nativescript.org/blog/nativescript-7-for-plugin-authors/)

Thank you :)