[xdg_directories] Update to stable NNBD release (#291)

Updates all dependencies to stable versions, and updates its own version
to stable.

Replaces `mockito`'s Fake with the new `test` Fake to reduce
dependencies (and since `mockito` doesn't yet have a stable NNBD
release).

packages/xdg_directories/CHANGELOG.md

@@ -1,20 +1,15 @@
-## [0.2.0-nullsafety.1] - Fix getUserDirectory
-
-* Fixes a regression due to the stdoutEncoding change
-  in the null-safety migration.
-
-## [0.2.0-nullsafety.0] - Migrated to null safety
+## 0.2.0
 
 * Migrated to null safety.
 
-## [0.1.2] - Reduce dependencies on external libraries.
+## 0.1.2
 
 * Broaden dependencies to allow nullsafety version of process, meta, and path to be OK.
 
-## [0.1.1] - Reduce dependencies on external libraries.
+## 0.1.1
 
 * Remove flutter, flutter_test from pubspec dependencies.
 
-## [0.1.0] - Initial Release
+## 0.1.0
 
 * Initial release includes all the features described in the README.md

packages/xdg_directories/pubspec.yaml

@@ -1,16 +1,15 @@
 name: xdg_directories
 description: A Dart package for reading XDG directory configuration information on Linux.
-version: 0.2.0-nullsafety.1
+version: 0.2.0
 homepage: https://github.com/flutter/packages/tree/master/packages/xdg_directories
 
 environment:
   sdk: ">=2.12.0-0 <3.0.0"
 
 dependencies:
-  meta: ^1.3.0-nullsafety.6
-  path: ^1.8.0-nullsafety.3
-  process: ^4.0.0-nullsafety.4
+  meta: ^1.3.0
+  path: ^1.8.0
+  process: ^4.0.0
 
 dev_dependencies:
-  mockito: ^5.0.0-nullsafety.1
-  test: ^1.16.0-nullsafety.13
+  test: ^1.16.0

packages/xdg_directories/test/xdg_directories_test.dart

@@ -5,9 +5,9 @@
 import 'dart:convert';
 import 'dart:io';
 
+import 'package:test/fake.dart';
 import 'package:test/test.dart';
 import 'package:path/path.dart' as path;
-import 'package:mockito/mockito.dart' show Fake;
 import 'package:process/process.dart';
 
 import 'package:xdg_directories/xdg_directories.dart' as xdg;