message: Fix plain text export saving
  This tweaks the MIME type of plain text exports so that the browser actually
  saves the file.
diff: @@ -105,7 +105,7 @@ export default abstract class Exporter {
  }
  protected downloadPlainText(fileName: string, text: string) {
  - const content = new Blob([text], { type: "text" });
  + const content = new Blob([text], { type: "text/plain" });
  saveAs(content, fileName);
  }
  