[cross_file] Stable null safety release (flutter#3593)

Author: mvanbeusekom

packages/cross_file/CHANGELOG.md

@@ -1,4 +1,4 @@
-## 0.3.0-nullsafety
+## 0.3.0
 
 * Migrated package to null-safety.
 * **breaking change** According to our unit tests, the API should be backwards-compatible. Some relevant changes were made, however:

packages/cross_file/pubspec.yaml

@@ -1,18 +1,18 @@
 name: cross_file
 description: An abstraction to allow working with files across multiple platforms.
 homepage: https://github.com/flutter/plugins/tree/master/packages/cross_file
-version: 0.3.0-nullsafety
+version: 0.3.0
 
 dependencies:
   flutter:
     sdk: flutter
-  meta: ^1.3.0-nullsafety.3
+  meta: ^1.3.0
 
 dev_dependencies:
   flutter_test:
     sdk: flutter
-  pedantic: ^1.10.0-nullsafety.3
+  pedantic: ^1.10.0
 
 environment:
-  sdk: ">=2.12.0-0 <3.0.0"
+  sdk: ">=2.12.0-259.9.beta <3.0.0"
   flutter: ">=1.22.0"