Update err-spec.md

docs/tutorial/err-spec.md

@@ -41,7 +41,7 @@ interface UniError {
 	errCode: number,
 	errMsg: string,
 	data?: Object,
-	cause?: SourceError | AggregateError
+	cause?: SourceError | UniAggregateError
 }
 
 //回调函数