Handle HTTP chunking across multi-byte boundaries

When a response contains multi-byte UTF-8 characters that cross chunk
boundaries, appending the two halves to the intermediate string results
in two Unicode Replacement Characters being inserted instead of the two
halves being joined.

Use StringDecoder to buffer the partial characters across chunks.

Resolves #22

src/utils.ts

@@ -1,6 +1,7 @@
 import { version } from "../version.ts";
 import https from "node:https";
 import qs from "node:querystring";
+import { StringDecoder } from "node:string_decoder";
 import { RequestTimeoutError } from "./errors.ts";
 
 /**
@@ -63,15 +64,17 @@ export function execute(
   return new Promise((resolve, reject) => {
     let timer: number;
     const req = https.get(url, (resp) => {
+      const decoder = new StringDecoder("utf8");
       let data = "";
 
       // A chunk of data has been recieved.
       resp.on("data", (chunk) => {
-        data += chunk;
+        data += decoder.write(chunk);
       });
 
       // The whole response has been received. Print out the result.
       resp.on("end", () => {
+        data += decoder.end();
         try {
           if (resp.statusCode == 200) {
             resolve(data);