Join should use UTF-8 Encoding

src/functions/join.ts

@@ -4,7 +4,7 @@ import { WithEncoding } from "./baseDefinitions";
 
 export function join(
     separator: string,
-    options?: WithEncoding & TransformOptions,
+    options: WithEncoding & TransformOptions = { encoding: "utf8" },
 ): Transform {
     let isFirstChunk = true;
     const decoder = new StringDecoder(options.encoding);