Position demo: Fixed usage of center positioning.

Author: scottgonzalez

demos/position/default.html

@@ -95,7 +95,7 @@
 		</select>
 		<select id="my_vertical">
 			<option value="top">top</option>
-			<option value="middle">center</option>
+			<option value="center">center</option>
 			<option value="bottom">bottom</option>
 		</select>
 	</div>
@@ -108,7 +108,7 @@
 		</select>
 		<select id="at_vertical">
 			<option value="top">top</option>
-			<option value="middle">center</option>
+			<option value="center">center</option>
 			<option value="bottom">bottom</option>
 		</select>
 	</div>