Update is/custom_jsonable.ts

Co-authored-by: Milly <[email protected]>

is/custom_jsonable.ts

@@ -11,7 +11,7 @@ export type CustomJsonable = {
 };
 
 /**
- * Returns true if `x` is ({@linkcode CustomJsonable}), false otherwise.
+ * Returns true if `x` is {@linkcode CustomJsonable}, false otherwise.
  *
  * Use {@linkcode [is/jsonable].isJsonable|isJsonable} to check if the type of `x` is a JSON-serializable.
  *