Fix a minor typo in the TextField.controller docs (#12267)

packages/flutter/lib/src/material/text_field.dart

diff --git a/packages/flutter/lib/src/material/text_field.dart b/packages/flutter/lib/src/material/text_field.dart
index 66e612a..09fa0f3 100644
--- a/packages/flutter/lib/src/material/text_field.dart
+++ b/packages/flutter/lib/src/material/text_field.dart
@@ -96,7 +96,7 @@
 
   /// Controls the text being edited.
   ///
-  /// If null, this widget will creates its own [TextEditingController].
+  /// If null, this widget will create its own [TextEditingController].
   final TextEditingController controller;
 
   /// Controls whether this widget has keyboard focus.