update tslint -> eslint

src/app/services/db.service.ts

@@ -1,19 +1,18 @@
 import {Injectable} from '@angular/core';
 import {AngularFirestore, AngularFirestoreCollection, AngularFirestoreDocument} from '@angular/fire/firestore';
 import {Observable} from 'rxjs';
+import {QueryFn} from '@angular/fire/firestore/interfaces';
 
 type CollectionPredicate<T> = string | AngularFirestoreCollection<T>;
 type DocumentPredicate<T> = string | AngularFirestoreDocument<T>;
 
 @Injectable({
-  providedIn: 'root'
+  providedIn: 'root',
 })
 export class DbService {
+  public constructor(private afs: AngularFirestore) {}
 
-  constructor(private afs: AngularFirestore) {
-  }
-
-  public col<T>(ref: CollectionPredicate<T>, queryFn?): AngularFirestoreCollection<T> {
+  public col<T>(ref: CollectionPredicate<T>, queryFn?: QueryFn): AngularFirestoreCollection<T> {
     return typeof ref === 'string' ? this.afs.collection<T>(ref, queryFn) : ref;
   }
 
@@ -23,10 +22,9 @@ export class DbService {
 
   public doc$<T>(ref: DocumentPredicate<T>): Observable<T> {
     return this.doc(ref).valueChanges({idField: 'id'});
-
   }
 
-  public col$<T>(ref: CollectionPredicate<T>, queryFn?): Observable<T[]> {
+  public col$<T>(ref: CollectionPredicate<T>, queryFn?: QueryFn): Observable<T[]> {
     return this.col(ref, queryFn).valueChanges({idField: 'id'});
   }
 }