Fix a typo. Thanks to Jon Biggar.

[SVN r48412]

tools/index.html

@@ -75,7 +75,7 @@
          <li>
            <a href="../libs/wave/doc/wave_driver.html">Wave</a> - A Standards conformant C/C++ 
 		   preprocessor usable on top of any other compiler. Usable for instance for the debugging 
-		   of the expansion of macros in your code or as a replacement for your build in 
+		   of the expansion of macros in your code or as a replacement for your built-in 
 		   preprocessor. <br>
       </li>
    </ul>
@@ -96,4 +96,4 @@ Distributed under the Boost Software License, Version 1.0.
 (See file <a href="../LICENSE_1_0.txt">LICENSE_1_0.txt</a>
 or <a href="http://www.boost.org/LICENSE_1_0.txt">www.boost.org/LICENSE_1_0.txt</a>) </p>
    </body>
-</html>
+</html>