message: Use *Sync dialog variants
  This has changed with Electron versions, Petmate's
  earlier dialogs were implicitly sync.
diff: @@ -318,7 +318,7 @@ export function dialogLoadWorkspace(
  const filters = [
  {name: 'Petmate workspace', extensions: ['petmate']},
  ]
  - const filename = dialog.showOpenDialog(window, {properties: ['openFile'], filters})
  + const filename = dialog.showOpenDialogSync(window, {properties: ['openFile'], filters})
  if (filename === undefined) {
  return
  }
  @@ -341,7 +341,7 @@ export function dialogSaveAsWorkspace(
  const filters = [
  {name: 'Petmate workspace file', extensions: ['petmate']},
  ];
  - const filename = dialog.showSaveDialog(window, {properties: ['openFile'], filters});
  + const filename = dialog.showSaveDialogSync(window, {properties: ['openFile'], filters});
  if (filename === undefined) {
  return;
  }
  @@ -355,7 +355,7 @@ export function dialogExportFile(fmt: FileFormat, framebufs: FramebufWithFont[],
  const filters = [
  {name: fmt.name, extensions: [fmt.ext]}
  ]
  - const filename = dialog.showSaveDialog(window, {properties: ['openFile'], filters})
  + const filename = dialog.showSaveDialogSync(window, {properties: ['openFile'], filters})
  if (filename === undefined) {
  return
  }
  @@ -370,7 +370,7 @@ export function dialogReadFile(type: FileFormat, loadFile: (data: Buffer) => voi
  const filters = [
  { name: type.name, extensions: [type.ext] }
  ]
  - const filename = dialog.showOpenDialog(window, {properties: ['openFile'], filters})
  + const filename = dialog.showOpenDialogSync(window, {properties: ['openFile'], filters})
  if (filename === undefined) {
  return
  }
  @@ -390,7 +390,7 @@ export function dialogImportFile(type: FileFormat, importFile: (fbs: Framebuf[])
  const filters = [
  { name: type.name, extensions: [type.ext] }
  ]
  - const filename = dialog.showOpenDialog(window, {properties: ['openFile'], filters})
  + const filename = dialog.showOpenDialogSync(window, {properties: ['openFile'], filters})
  if (filename === undefined) {
  return
  }
  