copy edit modal sheet demo (#20703)

examples/flutter_gallery/lib/demo/material/modal_bottom_sheet_demo.dart

diff --git a/examples/flutter_gallery/lib/demo/material/modal_bottom_sheet_demo.dart b/examples/flutter_gallery/lib/demo/material/modal_bottom_sheet_demo.dart
index 3aa1db7..8fdbf41 100644
--- a/examples/flutter_gallery/lib/demo/material/modal_bottom_sheet_demo.dart
+++ b/examples/flutter_gallery/lib/demo/material/modal_bottom_sheet_demo.dart
@@ -19,7 +19,7 @@
               return new Container(
                 child: new Padding(
                   padding: const EdgeInsets.all(32.0),
-                  child: new Text('This is the modal bottom sheet. Click anywhere to dismiss.',
+                  child: new Text('This is the modal bottom sheet. Tap anywhere to dismiss.',
                     textAlign: TextAlign.center,
                     style: new TextStyle(
                       color: Theme.of(context).accentColor,