[battery] relax the example app minimal required Flutter version  (#2189)

diff --git a/packages/battery/example/pubspec.yaml b/packages/battery/example/pubspec.yaml
index 0c57142..88f600b 100644
--- a/packages/battery/example/pubspec.yaml
+++ b/packages/battery/example/pubspec.yaml
@@ -13,6 +13,3 @@
 
 flutter:
   uses-material-design: true
-
-environment:
-  flutter: ">=1.9.1+hotfix.4 <2.0.0"