New color for cover block background

Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>

app/assets/stylesheets/framework/blocks.scss

@@ -76,7 +76,7 @@
 
 .cover-block {
   text-align: center;
-  background: #f7f8fa;
+  background: $background-color;
   margin: -$gl-padding;
   margin-bottom: 0;
   padding: 44px $gl-padding;