Migrate to Popper 2.x

[leunardo]

Hello,

I would like to migrate the package to use the new version of Popper.

We need to apply the instructions provided in https://popper.js.org/docs/v2/migration-guide/.

If you are interested in this change I can help with a pull request.

This change will introduce a breaking change in the package.

[castevinz]

And by the way to correct the ngcc compilation problems for Ivy (angular 9):

Error: Failed to compile entry-point ngx-popper (es2015 as esm2015) due to compilation errors:
node_modules/@angular/common/common.d.ts:115:22 - error NG6002: Appears in the NgModule.imports of NgxPopperModule, but could not be resolved to an NgModule class.

[tonysamperi]

@leunardo Just released [email protected] which is based on this one and now uses Popper 2 and Angular 8 (updating to Angular 9 and 10 in the next few days)
@castevinz shouldn't also incur in the error you reported!

demo here => https://tonysamperi.github.io/ngx-popperjs/