minima/_layout.scss: Remove black line on top (rust-gamedev#585)

Author: ozkriff

sass/_extra.scss

@@ -12,6 +12,11 @@ pre > code {
     background-color: inherit;
 }
 
+.site-header {
+    // To avoid a thick black line on top of the page.
+    border-top: none;
+}
+
 .intro {
     color: #ffffff;
     background-color: $brand-color;