fix stylesheet path in github page

Author: stomita

.storybook/head.html

@@ -1,7 +1,9 @@
 <script>
 (function() {
   var stylesheetUrl =
-    (/\.sbook\.io$/.test(location.hostname) ? "//mashmatrix.github.io/react-lightning-design-system" : "") +
+    (/\.sbook\.io$/.test(location.hostname) ? "//mashmatrix.github.io/react-lightning-design-system" :
+     location.hostname === "mashmatrix.github.io" ? "/react-lightning-design-system" :
+     "") +
     "/assets/styles/salesforce-lightning-design-system.min.css";
   var link = document.createElement('link');
   link.href = stylesheetUrl;