Fixed typo. (#2)

Author: radekmie

index.html

@@ -55,7 +55,7 @@ <h1>B-Tree <span class="label label-info reset-btree">Order <span id="order-disp
 
   <ul>
     <li>Every node has at most <em>m</em> children.</li>
-    <li>Every internal node has at least <em>ciel( m / 2 )</em> children.</li>
+    <li>Every internal node has at least <em>ceil( m / 2 )</em> children.</li>
     <li>The root node has at least 2 children if it's not a leaf.</li>
     <li>A non-leaf node with <em>k</em> children contains <em>k-1</em> keys.</li>
     <li>All leaves are on the same level.</li>