Update minimal dart sdk version

Author: renefloor

flutter_cache_manager/example/lib/plugin_example/file_info_widget.dart

@@ -20,19 +20,19 @@ class FileInfoWidget extends StatelessWidget {
       children: <Widget>[
         ListTile(
           title: const Text('Original URL'),
-          subtitle: Text(fileInfo.originalUrl ?? ''),
+          subtitle: Text(fileInfo.originalUrl),
         ),
         ListTile(
           title: const Text('Local file path'),
-          subtitle: Text(fileInfo.file.path ?? ''),
+          subtitle: Text(fileInfo.file.path),
         ),
         ListTile(
           title: const Text('Loaded from'),
-          subtitle: Text(fileInfo.source.toString() ?? ''),
+          subtitle: Text(fileInfo.source.toString()),
         ),
         ListTile(
           title: const Text('Valid Until'),
-          subtitle: Text(fileInfo.validTill.toIso8601String() ?? ''),
+          subtitle: Text(fileInfo.validTill.toIso8601String()),
         ),
         Padding(
           padding: const EdgeInsets.all(10),

flutter_cache_manager/example/pubspec.yaml

@@ -3,7 +3,7 @@ description: A project that showcases usage of flutter_cache_manager
 publish_to: none
 version: 1.0.0+1
 environment:
-  sdk: ^3.0.0
+  sdk: '>=2.17.0 <4.0.0'
 
 dependencies:
   baseflow_plugin_template: ^2.1.2
@@ -12,12 +12,12 @@ dependencies:
     sdk: flutter
   flutter_cache_manager:
     path: ../
-  url_launcher: ^6.1.11
+  url_launcher: ^6.1.10
 
 dev_dependencies:
   flutter_test:
     sdk: flutter
-  flutter_lints: ^2.0.2
+  flutter_lints: ^2.0.1
 
 flutter:
   uses-material-design: true

flutter_cache_manager/pubspec.yaml

@@ -6,7 +6,7 @@ topics:
   - cache
   - cache-manager
 environment:
-  sdk: '>=2.12.0 <4.0.0'
+  sdk: '>=2.17.0 <4.0.0'
 
 dependencies:
   clock: ^1.1.0
@@ -23,7 +23,7 @@ dependencies:
 
 dev_dependencies:
   build_runner: ^2.0.0
-  flutter_lints: ^2.0.2
+  flutter_lints: ^2.0.1
   flutter_test:
     sdk: flutter
   mockito: ^5.0.0