Use a better Dart link

Author: cuviper

text/0000-raw-identifiers.md

@@ -164,7 +164,7 @@ choose to stabilize it that way.  Perhaps `br#keyword` could be used for this,
 but that may not be a good intuitive relationship.
 
 [C#]: https://msdn.microsoft.com/en-us/library/aa664670(v=vs.71).aspx
-[Dart]: https://github.com/chalin/dart-spec-and-grammar/blob/6dafa1bc78ab85a4f35ce9b38e71f36b3986ee1a/doc/grammar-AUTOGENERATED-DO-NOT-EDIT.md#symbolLiteral
+[Dart]: https://www.dartlang.org/guides/language/language-tour#symbols
 [Kotlin]: https://kotlinlang.org/docs/reference/grammar.html
 [Scala]: https://www.scala-lang.org/files/archive/spec/2.13/01-lexical-syntax.html#identifiers
 [Swift]: https://developer.apple.com/library/content/documentation/Swift/Conceptual/Swift_Programming_Language/LexicalStructure.html