Enable compression for packaged zip (.foxe) files (#147)

JSZip default "compression" is STORE, you need to enable DEFLATE
explicitly. See
<https://stuk.github.io/jszip/documentation/api_jszip/generate_async.html#compression-and-compressionoptions-options>

src/package.ts

@@ -264,7 +264,7 @@ async function writeFoxe(baseDir: string, files: string[], outputFile: string):
   info(`Writing archive to ${outputFile}`);
   return await new Promise((c, e) => {
     zip
-      .generateNodeStream({ type: "nodebuffer", streamFiles: true })
+      .generateNodeStream({ type: "nodebuffer", streamFiles: true, compression: "DEFLATE" })
       .pipe(createWriteStream(outputFile, { encoding: "binary" }) as NodeJS.WritableStream)
       .on("error", e)
       .on("finish", c);