doc grammar fix for `prefer_const_declarations`

Change-Id: Ia05f0f6cc9b2283f624fa18deece924012fd9432
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/365880
Reviewed-by: Brian Wilkerson <brianwilkerson@google.com>
Commit-Queue: Phil Quitslund <pquitslund@google.com>
diff --git a/pkg/linter/lib/src/rules/prefer_const_declarations.dart b/pkg/linter/lib/src/rules/prefer_const_declarations.dart
index ccfe415..5c66e3e 100644
--- a/pkg/linter/lib/src/rules/prefer_const_declarations.dart
+++ b/pkg/linter/lib/src/rules/prefer_const_declarations.dart
@@ -14,8 +14,8 @@
 const _details = r'''
 **PREFER** using `const` for constant-valued declarations.
 
-Constant declarations are more hot-reload friendly and allows
-the value to be used in other constant expressions.
+Constant declarations are more hot-reload friendly and allow
+values to be used in other constant expressions.
 
 **BAD:**
 ```dart