fix well to card

docs/components/collapse.md

@@ -31,7 +31,7 @@ You can use a link with the `href` attribute, or a button with the `data-target`
   </button>
 </p>
 <div class="collapse" id="collapseExample">
-  <div class="well">
+  <div class="card card-block">
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   </div>
 </div>