Use only named exports of @google-cloud/firestore (#471)

Author: merlinnot

src/firebase-namespace.ts

@@ -375,7 +375,7 @@ export class FirebaseNamespace {
     const fn: FirebaseServiceNamespace<Firestore> = (app?: FirebaseApp) => {
       return this.ensureApp(app).firestore();
     };
-    return Object.assign(fn, require('@google-cloud/firestore'));
+    return Object.assign(fn, require('@google-cloud/firestore').Firestore);
   }
 
   /**

src/firestore/firestore.ts

@@ -115,7 +115,7 @@ function initFirestore(app: FirebaseApp): Firestore {
   let firestoreDatabase: typeof Firestore;
   try {
     // Lazy-load the Firestore implementation here, which in turns loads gRPC.
-    firestoreDatabase = require('@google-cloud/firestore');
+    firestoreDatabase = require('@google-cloud/firestore').Firestore;
   } catch (err) {
     throw new FirebaseFirestoreError({
       code: 'missing-dependencies',