[android_alarm_manager] update dart deps lower bound to 2.1.0 (#2747)

Author: Chris Yang

packages/android_alarm_manager/CHANGELOG.md

@@ -1,3 +1,7 @@
+## 0.4.5+11
+
+* Update lower bound of dart dependency to 2.1.0.
+
 ## 0.4.5+10
 
 * Declare API stability and compatibility with `1.0.0` (more details at: https://github.com/flutter/flutter/wiki/Package-migration-to-1.0.0).

packages/android_alarm_manager/pubspec.yaml

@@ -4,7 +4,7 @@ description: Flutter plugin for accessing the Android AlarmManager service, and
 # 0.4.y+z is compatible with 1.0.0, if you land a breaking change bump
 # the version to 2.0.0.
 # See more details: https://github.com/flutter/flutter/wiki/Package-migration-to-1.0.0
-version: 0.4.5+10
+version: 0.4.5+11
 homepage: https://github.com/flutter/plugins/tree/master/packages/android_alarm_manager
 
 dependencies:
@@ -24,5 +24,5 @@ flutter:
         pluginClass: AndroidAlarmManagerPlugin
 
 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"