bump version constraints in pubspec and readme

Author: clangenb

README.md

@@ -28,10 +28,10 @@ Encointer wallet and client for mobile phones
 </p>
 
 ### Requirements
-- Dart sdk: ">=3.2.0 <3.0.0"
-- flutter: "3.16.3"
-- Android: minSdkVersion 17
-- iOS: --ios-language swift, Xcode version >= 14.3
+- Dart sdk: ">=3.2.0 <4.0.0"
+- flutter: "3.27.1"
+- Android: minSdkVersion 21
+- iOS: --ios-language swift, Xcode version >= 15.2
 
 # Build Instructions
 

pubspec.yaml

@@ -3,7 +3,7 @@ description: EncointerWallet made with Flutter.
 
 environment:
   sdk: ">=3.2.0 <4.0.0"
-  flutter: "3.19.0"
+  flutter: "3.27.1"
 
 dev_dependencies:
   melos: 3.4.0