Upgrade to Electron 4.2.11

Fix #65

Notes:
  * Deprecation of `app.makeSingleInstance` https://github.com/electron/electron/blob/master/docs/api/breaking-changes.md#appmakesingleinstance
  * On Arch Linux with OpenBox, `app.dock` is `undefined`
  * Version 1.8.2 of Electron crashes with `Harfbuzz version too old`, but
    not Electron 1.8.3

main.ts

@@ -47,13 +47,14 @@ bugsnag.register('032040bba551785c7846442332cc067f', {
   releaseStage: releaseStage
 })
 
-const shouldQuit = app.makeSingleInstance((commandLine, workingDirectory) => {
+const shouldQuit = app.requestSingleInstanceLock()
+app.on('second-instance', (event, commandLine, workingDirectory) => {
   // Someone tried to run a second instance, we should focus our window.
   if (displayManager) {
     displayManager.showMain()
   }
 })
-if (shouldQuit) {
+if (!shouldQuit) {
   app.exit()
 }
 
@@ -191,7 +192,9 @@ function newTransparentOnTopWindow(
 }
 
 function onReady() {
-  app.dock.hide() // needed to support fullscreen mode in OS X, see https://github.com/electron/electron/issues/3302
+  if (app.dock) {
+    app.dock.hide() // needed to support fullscreen mode in OS X, see https://github.com/electron/electron/issues/3302
+  }
   displayManager = new DisplayManager(
     transparencyDisabled,
     bugsnag,