Remove role unnecessary

Created by: adammacias

I used validator.w3.org and it show that...

docs/_includes/nav/main.html

-<header class="navbar navbar-static-top bs-docs-nav" id="top" role="banner">
+<header class="navbar navbar-static-top bs-docs-nav" id="top">
   <div class="container">
     <div class="navbar-header">
       <button class="navbar-toggle collapsed" type="button" data-toggle="collapse" data-target="#bs-navbar" aria-controls="bs-navbar" aria-expanded="false">

docs/_includes/footer.html

 <!-- Footer
 ================================================== -->
-<footer class="bs-docs-footer" role="contentinfo">
+<footer class="bs-docs-footer">
   <div class="container">
     {% include social-buttons.html %}
 

docs/index.html

@@ -4,7 +4,7 @@ title: Bootstrap · The world's most popular mobile-first and responsive f
 ---
 
 
-<main class="bs-docs-masthead" id="content" role="main" tabindex="-1">
+<main class="bs-docs-masthead" id="content" tabindex="-1">
   <div class="container">
     <span class="bs-docs-booticon bs-docs-booticon-lg bs-docs-booticon-outline">B</span>
     <p class="lead">Bootstrap is the most popular HTML, CSS, and JS framework for developing responsive, mobile first projects on the web.</p>