Sample: Fix prebid js loading bug on sample html page (prebid#3792)

Author: And1sS

sample/001_banner/pbjs.html

@@ -12,8 +12,8 @@
             border-style: solid;
         }
     </style>
-    <script src="//cdn.jsdelivr.net/npm/prebid.js@latest/dist/not-for-prod/prebid.js"></script>
-    <script>
+    <script src="//cdn.jsdelivr.net/npm/prebid.js@latest/dist/not-for-prod/prebid.js" defer></script>
+    <script defer>
 
         var sizes = [
             [300, 250],
@@ -77,7 +77,7 @@
         }
 
     </script>
-    <script>
+    <script defer>
         var pbjs = pbjs || {};
         pbjs.que = pbjs.que || [];