[shared_preferences] Bump version for NNBD stable (flutter#3586)

Author: stuartmorgan-g

packages/shared_preferences/shared_preferences_platform_interface/CHANGELOG.md

@@ -1,4 +1,4 @@
-## 2.0.0-nullsafety
+## 2.0.0
 
 * Migrate to null safety.
 

packages/shared_preferences/shared_preferences_platform_interface/pubspec.yaml

@@ -1,7 +1,7 @@
 name: shared_preferences_platform_interface
 description: A common platform interface for the shared_preferences plugin.
 homepage: https://github.com/flutter/plugins/tree/master/packages/shared_preferences/shared_preferences_platform_interface
-version: 2.0.0-nullsafety
+version: 2.0.0
 
 dependencies:
   flutter:
@@ -10,8 +10,8 @@ dependencies:
 dev_dependencies:
   flutter_test:
     sdk: flutter
-  pedantic: ^1.10.0-nullsafety
+  pedantic: ^1.10.0
 
 environment:
-  sdk: ">=2.12.0-0 <3.0.0"
+  sdk: ">=2.12.0-259.9.beta <3.0.0"
   flutter: ">=1.12.8"