fix(theme): fix broken search index when hosting docs locally

Update default.hbs to retrieve search.json instead of legacy seach.js when loaded over file://
protocol

theme/v2/layouts/default.hbs

@@ -43,7 +43,7 @@
 
 <div class="overlay"></div>
 <script src="{{relativeURL "assets/js/main.js"}}"></script>
-<script>if (location.protocol == 'file:') document.write('<script src="{{relativeURL "assets/js/search.js"}}"><' + '/script>');</script>
+<script>if (location.protocol == 'file:') document.write('<script src="{{relativeURL "assets/js/search.json"}}"><' + '/script>');</script>
 
 {{> analytics}}