package.json compatible with Angular 4

[istreeter]

I would like to update my app to angular 4, which is backwards compatible with angular 2. Currently I cannot update by I get this error message:

npm WARN [email protected] requires a peer of @angular/core@^2.0.0 but none was installed.

This can be fixed by changing peerDependencies to "^2.0.0 || ^4.0.0"

It would be great if you could accept this pull request so that I can update my app whilst still using ngx-popover.