Increase fixed layout width to 1280px

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

app/assets/stylesheets/framework/variables.scss

@@ -19,7 +19,7 @@ $border-color: #dce0e6;
 $table-border-color: #eef0f2;
 $background-color: #F7F8FA;
 $header-height: 58px;
-$fixed-layout-width: 1200px;
+$fixed-layout-width: 1280px;
 $gl-gray: #7f8fa4;
 $gl-padding: 16px;
 $gl-avatar-size: 46px;