Fixed application still running after exit on Linux (#1996) (#3486)

src/browser.js

@@ -49,7 +49,7 @@ app.on('ready', function () {
   });
 
 
-  if (os.platform() === 'win32') {
+  if (os.platform() === 'win32' || os.platform() === 'linux') {
     mainWindow.on('close', function (e) {
       mainWindow.webContents.send('application:quitting');
       if(!exiting){

src/components/Header.react.js

@@ -44,7 +44,7 @@ var Header = React.createClass({
     }
   },
   handleClose: function () {
-    if (util.isWindows()) {
+    if (util.isWindows() || util.isLinux()) {
       remote.getCurrentWindow().close();
     } else {
       remote.getCurrentWindow().hide();