rev the min dart sdk dep in the templates to 2.1.0 (#26235)

diff --git a/packages/flutter_tools/templates/app/pubspec.yaml.tmpl b/packages/flutter_tools/templates/app/pubspec.yaml.tmpl
index 229bb06..9f9b2c3 100644
--- a/packages/flutter_tools/templates/app/pubspec.yaml.tmpl
+++ b/packages/flutter_tools/templates/app/pubspec.yaml.tmpl
@@ -15,7 +15,7 @@
 {{/withPluginHook}}
 
 environment:
-  sdk: ">=2.0.0-dev.68.0 <3.0.0"
+  sdk: ">=2.1.0 <3.0.0"
 
 dependencies:
   flutter:
diff --git a/packages/flutter_tools/templates/module/common/pubspec.yaml.tmpl b/packages/flutter_tools/templates/module/common/pubspec.yaml.tmpl
index 71ca18f..165c2f3 100644
--- a/packages/flutter_tools/templates/module/common/pubspec.yaml.tmpl
+++ b/packages/flutter_tools/templates/module/common/pubspec.yaml.tmpl
@@ -14,7 +14,7 @@
 version: 1.0.0+1
 
 environment:
-  sdk: ">=2.0.0-dev.68.0 <3.0.0"
+  sdk: ">=2.1.0 <3.0.0"
 
 dependencies:
   flutter:
diff --git a/packages/flutter_tools/templates/package/pubspec.yaml.tmpl b/packages/flutter_tools/templates/package/pubspec.yaml.tmpl
index 69cbd52..108d360 100644
--- a/packages/flutter_tools/templates/package/pubspec.yaml.tmpl
+++ b/packages/flutter_tools/templates/package/pubspec.yaml.tmpl
@@ -5,7 +5,7 @@
 homepage:
 
 environment:
-  sdk: ">=2.0.0-dev.68.0 <3.0.0"
+  sdk: ">=2.1.0 <3.0.0"
 
 dependencies:
   flutter:
diff --git a/packages/flutter_tools/templates/plugin/pubspec.yaml.tmpl b/packages/flutter_tools/templates/plugin/pubspec.yaml.tmpl
index 31562b9..a4f1e85 100644
--- a/packages/flutter_tools/templates/plugin/pubspec.yaml.tmpl
+++ b/packages/flutter_tools/templates/plugin/pubspec.yaml.tmpl
@@ -5,7 +5,7 @@
 homepage:
 
 environment:
-  sdk: ">=2.0.0-dev.68.0 <3.0.0"
+  sdk: ">=2.1.0 <3.0.0"
 
 dependencies:
   flutter: