update tslint -> eslint

src/app/modules/songs/services/file.service.ts

@@ -4,22 +4,17 @@ import {Observable} from 'rxjs';
 import {FileDataService} from './file-data.service';
 
 @Injectable({
-  providedIn: 'root'
+  providedIn: 'root',
 })
 export class FileService {
-
-  constructor(
-    private storage: AngularFireStorage,
-    private fileDataService: FileDataService
-  ) {
-  }
+  public constructor(private storage: AngularFireStorage, private fileDataService: FileDataService) {}
 
   public getDownloadUrl(path: string): Observable<string> {
     const ref = this.storage.ref(path);
-    return ref.getDownloadURL();
+    return ref.getDownloadURL() as Observable<string>;
   }
 
-  public async delete(path: string, songId: string, fileId: string) {
+  public async delete(path: string, songId: string, fileId: string): Promise<void> {
     const ref = this.storage.ref(path);
     await ref.delete().toPromise();
     await this.fileDataService.delete(songId, fileId);