Set maxlength for search input to 64 chars

fixes  adityatelange#1329

Author: adityatelange

layouts/_default/search.html

@@ -22,7 +22,7 @@ <h1>{{- (printf "%s&nbsp;" .Title ) | htmlUnescape -}}
 
 <div id="searchbox">
     <input id="searchInput" autofocus placeholder="{{ .Params.placeholder | default (printf "%s ↵" .Title) }}"
-        aria-label="search" type="search" autocomplete="off">
+        aria-label="search" type="search" autocomplete="off" maxlength="64">
     <ul id="searchResults" aria-label="search results"></ul>
 </div>