[camera] Update lower bound of dart dependency to 2.1.0. (flutter#2749)

Author: Chris Yang

packages/camera/CHANGELOG.md

@@ -1,3 +1,7 @@
+## 0.5.8+1
+
+* Update lower bound of dart dependency to 2.1.0.
+
 ## 0.5.8
 
 * Remove Android dependencies fallback.

packages/camera/pubspec.yaml

@@ -2,7 +2,7 @@ name: camera
 description: A Flutter plugin for getting information about and controlling the
   camera on Android and iOS. Supports previewing the camera feed, capturing images, capturing video,
   and streaming image buffers to dart.
-version: 0.5.8
+version: 0.5.8+1
 
 homepage: https://github.com/flutter/plugins/tree/master/packages/camera
 
@@ -29,5 +29,5 @@ flutter:
         pluginClass: CameraPlugin
 
 environment:
-  sdk: ">=2.0.0-dev.28.0 <3.0.0"
+  sdk: ">=2.1.0 <3.0.0"
   flutter: ">=1.12.13+hotfix.5 <2.0.0"