Fix fetcher not close file descriptor correctly (#889)

* Fix fetcher not close file descriptor correctly
* Call Sync() before chmod

environments/fetcher/fetcher.go

@@ -105,10 +105,19 @@ func downloadUrl(url string, localPath string) error {
 	if err != nil {
 		return err
 	}
+	defer w.Close()
+
 	_, err = io.Copy(w, resp.Body)
 	if err != nil {
 		return err
 	}
+
+	// flushing write buffer to file
+	err = w.Sync()
+	if err != nil {
+		return err
+	}
+
 	err = os.Chmod(localPath, 0600)
 	if err != nil {
 		return err