Fixed missing bootstrap.min.css in some chapter 3 demos.

chapter3/06navbar.html

@@ -5,6 +5,7 @@
   <meta charset="utf-8"/>
   <meta http-equiv="X-UA-COMPATIBLE" content="IE=Edge"/>
   <meta name="viewport" content="width=device-width, initial-scale=1"/>
+  <link rel="stylesheet" href="../css/bootstrap.min.css"/>
   <link rel="stylesheet" href="styles.css" />
   <!--[if lt IE 9]>
   <script src="../js/html5shiv.3-7-0.js"></script>

chapter3/07breadcrumbs.html

@@ -5,6 +5,7 @@
   <meta charset="utf-8"/>
   <meta http-equiv="X-UA-COMPATIBLE" content="IE=Edge"/>
   <meta name="viewport" content="width=device-width, initial-scale=1"/>
+  <link rel="stylesheet" href="../css/bootstrap.min.css"/>
   <link rel="stylesheet" href="styles.css" />
   <!--[if lt IE 9]>
   <script src="../js/html5shiv.3-7-0.js"></script>