Add File > Quit for Linux users with broken system trays

Works around #303

main/menu.js

@@ -155,10 +155,7 @@ function showOpenTorrentAddress () {
 }
 
 function getAppMenuTemplate () {
-  var template = [
-    {
-      label: 'File',
-      submenu: [
+  var fileMenu = [
     {
       label: 'Create New Torrent...',
       accelerator: 'CmdOrCtrl+N',
@@ -178,13 +175,24 @@ function getAppMenuTemplate () {
       type: 'separator'
     },
     {
-          label: process.platform === 'darwin'
-            ? 'Close Window'
-            : 'Close',
+      label: process.platform === 'windows' ? 'Close' : 'Close Window',
       accelerator: 'CmdOrCtrl+W',
       role: 'close'
     }
   ]
+
+  // File > Quit for Linux users with distros where the system tray is broken
+  if (process.platform === 'linux') {
+    fileMenu.push({
+      label: 'Quit',
+      click: () => app.quit()
+    })
+  }
+
+  var template = [
+    {
+      label: 'File',
+      submenu: fileMenu
     },
     {
       label: 'Edit',