revamp narrow jumbotron to avoid conflicts with docs .masthead

docs/examples/jumbotron-narrow.html

@@ -12,7 +12,7 @@ title: Narrow page template
   }
 
   /* Everything but the jumbotron gets side spacing for mobile-first views */
-  .masthead,
+  .header,
   .marketing,
   .footer {
     padding-left: 15px;
@@ -20,11 +20,11 @@ title: Narrow page template
   }
 
   /* Custom page header */
-  .masthead {
+  .header {
     border-bottom: 1px solid #e5e5e5;
   }
   /* Make the masthead heading the same height as the navigation */
-  .masthead h3 {
+  .header h3 {
     margin-top: 0;
     margin-bottom: 0;
     line-height: 40px;
@@ -64,14 +64,14 @@ title: Narrow page template
   /* Responsive: Portrait tablets and up */
   @media screen and (min-width: 768px) {
     /* Remove the padding we set earlier */
-    .masthead,
+    .header,
     .marketing,
     .footer {
       padding-left: 0;
       padding-right: 0;
     }
     /* Space out the masthead */
-    .masthead {
+    .header {
       margin-bottom: 30px;
     }
   }
@@ -80,7 +80,7 @@ title: Narrow page template
 
 
 <div class="container-narrow">
-  <div class="masthead">
+  <div class="header">
     <ul class="nav nav-pills pull-right">
       <li class="active"><a href="#">Home</a></li>
       <li><a href="#">About</a></li>