Recommend using runtimeType in hash_and_equals (#1943)

> Using `is` in `operator ==` is usually wrong as it makes the `==` operator asymmetric.
dart-lang/sdk#36004 (comment)

Author: micimize

lib/src/rules/hash_and_equals.dart

@@ -39,7 +39,10 @@ class Better {
   Better(this.value);
 
   @override
-  bool operator ==(Object other) => other is Better && other.value == value;
+  bool operator ==(Object other) =>
+      other is Better &&
+      other.runtimeType == runtimeType &&
+      other.value == value;
 
   @override
   int get hashCode => value.hashCode;