remove tabindex=-1 as it was causing a weird select state in latest safari on...

remove tabindex=-1 as it was causing a weird select state in latest safari on yosemite when clicking anywhere in the negative space of the header

docs/index.html

@@ -3,7 +3,7 @@ layout: home
 title: Bootstrap · The world's most popular mobile-first and responsive front-end framework.
 ---
 
-<main class="bd-masthead" id="content" role="main" tabindex="-1">
+<main class="bd-masthead" id="content" role="main">
   <div class="container">
     {% include nav-home.html %}