osdWindow: Fix blurriness at certain resolutions

The y position wasn't rounded, leading to some blurriness at vertical
resolutions that aren't a multiple of 4 (e.g. 1050).

https://bugzilla.gnome.org/show_bug.cgi?id=782011

js/ui/osdWindow.js

@@ -204,7 +204,7 @@ var OsdWindow = new Lang.Class({
 
         let scaleFactor = St.ThemeContext.get_for_stage(global.stage).scale_factor;
         this._icon.icon_size = popupSize / (2 * scaleFactor);
-        this._box.translation_y = monitor.height / 4;
+        this._box.translation_y = Math.round(monitor.height / 4);
         this._boxConstraint.minSize = popupSize;
     }
 });