use absolute positioning for slide number

css/reveal.css

@@ -460,7 +460,7 @@ body {
  * SLIDE NUMBER
  *********************************************/
 .reveal .slide-number {
-  position: fixed;
+  position: absolute;
   display: block;
   right: 8px;
   bottom: 8px;

css/reveal.scss

@@ -556,7 +556,7 @@ $controlsArrowAngleActive: 36deg;
  *********************************************/
 
 .reveal .slide-number {
-	position: fixed;
+	position: absolute;
 	display: block;
 	right: 8px;
 	bottom: 8px;