fix: mobile lint issues

gmus-mobile/Dockerfile

@@ -26,6 +26,7 @@ RUN mkdir app
 WORKDIR app
 
 COPY . .
+RUN touch .env
 USER root
 RUN chown -R developer:developer /home/developer/app
 USER developer

gmus-mobile/lib/components/artists.dart

@@ -5,8 +5,6 @@ import 'package:http/http.dart' as http;
 
 import '../utils/url.dart';
 
-import './spinner.dart';
-
 Future<List<String>> fetchArtists(String apiUrl) async {
   final response = await http.get(formattedUrl(apiUrl, '/artists'));