Fix turbolink-spinner for light theme

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

app/assets/stylesheets/sections/header.scss

@@ -46,6 +46,11 @@ header {
       }
     }
+    .turbolink-spinner {
+      font-size: 20px;
+      margin-right: 10px;
+    }
+
     @media (max-width: $screen-xs-max) {
       border-width: 0;
       font-size: 18px;
@@ -196,8 +201,6 @@ header {
     .turbolink-spinner {
       color: #FFF;
-      font-size: 22px;
-      margin-right: 10px;
     }
     .search {