Center images in carousel example

In order to see the changes, you must shrink the browser to below the md threshold.

docs/examples/carousel/index.html

@@ -160,7 +160,7 @@
           <p class="lead">Donec ullamcorper nulla non metus auctor fringilla. Vestibulum id ligula porta felis euismod semper. Praesent commodo cursus magna, vel scelerisque nisl consectetur. Fusce dapibus, tellus ac cursus commodo.</p>
         </div>
         <div class="col-md-5">
-          <img class="featurette-image img-responsive" data-src="holder.js/500x500/auto" alt="Generic placeholder image">
+          <img class="featurette-image img-responsive center-block" data-src="holder.js/500x500/auto" alt="Generic placeholder image">
         </div>
       </div>
 
@@ -168,7 +168,7 @@
 
       <div class="row featurette">
         <div class="col-md-5">
-          <img class="featurette-image img-responsive" data-src="holder.js/500x500/auto" alt="Generic placeholder image">
+          <img class="featurette-image img-responsive center-block" data-src="holder.js/500x500/auto" alt="Generic placeholder image">
         </div>
         <div class="col-md-7">
           <h2 class="featurette-heading">Oh yeah, it's that good. <span class="text-muted">See for yourself.</span></h2>
@@ -184,7 +184,7 @@
           <p class="lead">Donec ullamcorper nulla non metus auctor fringilla. Vestibulum id ligula porta felis euismod semper. Praesent commodo cursus magna, vel scelerisque nisl consectetur. Fusce dapibus, tellus ac cursus commodo.</p>
         </div>
         <div class="col-md-5">
-          <img class="featurette-image img-responsive" data-src="holder.js/500x500/auto" alt="Generic placeholder image">
+          <img class="featurette-image img-responsive center-block" data-src="holder.js/500x500/auto" alt="Generic placeholder image">
         </div>
       </div>