Update index.html

Fixed spelling error on "customisablity". Changed to customizability.

index.html

@@ -118,7 +118,7 @@ <h2 class="about__header">No clever tagline needed</h2>
           Lawnchair is a supercharged version of
           the Pixel Launcher you know and love. Being an open-source project,
           you get all the latest Pixel Launcher features shipped by Google in
-          their latest Android release, plus added customisablity. The best
+          their latest Android release, plus added customizability. The best
           part? No root required!
         </div>
       </div>