fix snippet link

Author: StuartMosquera

docs/fsharp/language-reference/compiler-messages/fs0067.md

@@ -18,7 +18,7 @@ Redundant Type test:
 
 Redundant Downcast:
 
-[!code-fsharp[FS0067-redundant-downcast](~/samples/snippets/fsharp/compiler-messages/fs0003.fsx#L11-L18)]
+[!code-fsharp[FS0067-redundant-downcast](~/samples/snippets/fsharp/compiler-messages/fs0067.fsx#L11-L18)]
 
 The two examples above cause the compiler to display the following message: