change title of demo

docs/demo/pairing.html

@@ -11,7 +11,7 @@
 <div>
 library status <span name="status">initializing...</span>
 </div>
-<h2>pairing</h2>
+<h2>optimal Ate pairing over 256-bit BN curve</h2>
 <button type="text" onclick="TestPairing()">test Pairing</button>
 <div>
 a = <input type="text" name="a" value="3"><br>