[gnome-shell] keyboard: Minor cleanup

[verdre <jonasd src gnome org>]

commit 2b7015179418be402853633f79a06f12181421ad
Author: Florian Müllner <fmuellner gnome org>
Date:   Sat Apr 4 02:00:35 2020 +0200

    keyboard: Minor cleanup
    
    Use the more concise operator shorthand.
    
    https://gitlab.gnome.org/GNOME/gnome-shell/-/merge_requests/1177

 js/ui/keyboard.js | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)
---
diff --git a/js/ui/keyboard.js b/js/ui/keyboard.js
index 7ce8668023..4af2b18c47 100644
--- a/js/ui/keyboard.js
+++ b/js/ui/keyboard.js
@@ -722,7 +722,7 @@ var EmojiPager = GObject.registerClass({
 
     _onPan(action) {
         let [dist_, dx, dy_] = action.get_motion_delta(0);
-        this.delta = this.delta + dx;
+        this.delta += dx;
 
         if (this._currentKey != null) {
             this._currentKey.cancel();