Allow the stable 2.0 SDK (#35)

Update SDK and package:test constraints.
diff --git a/CHANGELOG.md b/CHANGELOG.md
index ad6d777..68d89da 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,3 +1,7 @@
+# 1.2.2
+
+* Allow the stable 2.0 SDK.
+
 # 1.2.1
 
 * Updated SDK version to 2.0.0-dev.17.0
diff --git a/pubspec.yaml b/pubspec.yaml
index 1b84732..dd721a6 100644
--- a/pubspec.yaml
+++ b/pubspec.yaml
@@ -1,5 +1,5 @@
 name: oauth2
-version: 1.2.1
+version: 1.2.2
 author: Dart Team <misc@dartlang.org>
 homepage: https://github.com/dart-lang/oauth2
 description: >
@@ -7,10 +7,10 @@
   behalf of a user, and making authorized HTTP requests with the user's
   OAuth2 credentials.
 environment:
-  sdk: '>=2.0.0-dev.17.0 <2.0.0'
+  sdk: '>=2.0.0-dev.17.0 <3.0.0'
 dependencies:
   collection: '^1.5.0'
   http: '>=0.11.0 <0.12.0'
   http_parser: '>=1.0.0 <4.0.0'
 dev_dependencies:
-  test: '>=0.12.0 <0.13.0'
+  test: ^1.0.0