style: Use red for anchor.js

Author: toshimaru

src/_sass/railsdoc.scss

@@ -243,10 +243,10 @@ code {
 }
 
 .anchorjs-link {
-  color: #AAAAAA;
+  color: $red;
 
   &:hover {
-    color: $red;
+    color: #ee0000;
     text-decoration: none;
   }
 }