Incorrect firestore import throws Typescript error

[Csaba Illes]

Describe your environment

• Operating System version: MacOS
• Browser version: Chrome 86
• Firebase library: firebase 8.0.0
• GeoFirestore version: 4.3.0

Describe the problem

After upgrading to latest geofire and firebase libraries, I get the following Typescript error:

    ERROR in node_modules/geofirestore-core/dist/definitions.d.ts:2:10 - error TS2614: 
Module '"../../firebase"' has no exported member 'firestore'. 
Did you mean to use 'import firestore from "../../firebase"' instead?

    2 import { firestore as webfirestore } from 'firebase/app';

Describe the bug

firestore is probably not imported correctly in the definition file.

[Marc-Antoine Roberge]

same for me.

[Marc-Antoine Roberge]

I fixed it manually by changing definitions.d.ts file import to import firebase from 'firebase/app'; and replacing old usage with something similar to firebase.firestore.CollectionReference;

[Marc-Antoine Roberge]

I created this PR to fix this issue. Hope it gets through.