Update default_about.liquid

Author: sawhney-medha

_layouts/default_about.liquid

@@ -16,7 +16,7 @@
 
   <div class="header-background">
     <div class="img" style="
-      background-image: url('/assets/img/lab_header_1.jpeg');
+      background-image: url('/assets/img/lab_header_1.jpg');
       background-repeat: no-repeat;
       background-size: contain;
       background-position: top center;