fix: use relative import for version.dart

Author: emyller

lib/src/flagsmith_client.dart

@@ -8,7 +8,7 @@ import 'package:flutter_client_sse/flutter_client_sse.dart';
 import 'package:rxdart/subjects.dart';
 
 import '../flagsmith.dart';
-import 'package:flagsmith/src/version.dart';
+import 'version.dart';
 
 /// Flagsmith client initialization
 ///