Fixes responsive header background image width

Expanded the width of the header background image so it fills in the blank margin at the 760px media query.

Author: John Fox

src/scenes/home/home.css

@@ -22,7 +22,7 @@
 
 @media screen and (max-width: 760px) {
   .backgroundImage {
-    background-size: auto 50%;
+    background-size: auto 75%;
     background-attachment: fixed;
   }
 }
@@ -32,4 +32,4 @@
     background-size: auto 75%;
     background-attachment: fixed;
   }
-}
+}