[gnome-shell-extensions] cleanup: Use operator shorthands where possible

[Florian Müllner <fmuellner src gnome org>]

commit b6d02f8e1fce0b46d9353db6a4631ec931e7ae88
Author: Florian Müllner <fmuellner gnome org>
Date:   Wed Aug 7 04:59:02 2019 +0200

    cleanup: Use operator shorthands where possible
    
    Shorthands like a += b are well-established, so prefer them over the
    less concise a = a + b.
    
    https://gitlab.gnome.org/GNOME/gnome-shell-extensions/merge_requests/91

 extensions/native-window-placement/extension.js | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)
---
diff --git a/extensions/native-window-placement/extension.js b/extensions/native-window-placement/extension.js
index dfe4165..ed319f7 100644
--- a/extensions/native-window-placement/extension.js
+++ b/extensions/native-window-placement/extension.js
@@ -206,8 +206,8 @@ class NaturalLayoutStrategy extends Workspace.LayoutStrategy {
             1.0);
 
         // Make bounding rect fill the screen size for later steps
-        bounds.x = bounds.x - (areaRect.width - bounds.width * scale) / 2;
-        bounds.y = bounds.y - (areaRect.height - bounds.height * scale) / 2;
+        bounds.x -= (areaRect.width - bounds.width * scale) / 2;
+        bounds.y -= (areaRect.height - bounds.height * scale) / 2;
         bounds.width = areaRect.width / scale;
         bounds.height = areaRect.height / scale;