Applied suggestion from code review

Author: Robert-SD

pubspec.yaml

@@ -20,8 +20,8 @@ dependencies:
   flutter:
     sdk: flutter
   plugin_platform_interface: ^2.1.8
-  pay: 3.2.1 # v3.3.0+ requires Android minSDK 23
-  pay_android: 3.1.1 # v3.2.0+ requires Android minSDK 23
+  pay: '>=3.2.1 <3.3.0' # v3.3.0+ requires Android minSDK 23
+  pay_android: '>=3.1.1 <3.2.0' # v3.2.0+ requires Android minSDK 23
 
 dev_dependencies:
   flutter_test: