Fix mime type for compressed client-side extensions

In Firefox using the gzip mime type will (probably correctly) cause it
not to decompress while in Chromium it still will (incorrectly).

src/node/http.ts

@@ -241,7 +241,7 @@ export abstract class HttpProvider {
       stream = compress
       headers["content-encoding"] = "gzip"
     }
-    return { stream, filePath, mime: "application/gzip", cache: true, headers }
+    return { stream, filePath, mime: "application/x-tar", cache: true, headers }
   }
 
   /**