[lldb] Fix ninja URL

The old URL is a 404 now. Pointed out by Smirftsch1 on IRC.

git-svn-id: https://llvm.org/svn/llvm-project/lldb/trunk@299845 91177308-0d34-0410-b5e6-96231b3b80d8

www/build.html

@@ -62,7 +62,7 @@ <h2>Required Dependencies</h2>
                 versions of Python can be made to work by compiling your own distribution from source,
                 but this workflow is unsupported and you are own your own.
               </li>
-              <li><a href="http://martine.github.io/ninja/">Ninja build tool</a> (strongly recommended)</li>
+              <li><a href="https://ninja-build.org/">Ninja build tool</a> (strongly recommended)</li>
               <li><a href="http://gnuwin32.sourceforge.net/">GnuWin32</a></li>
               <li><a href="http://www.swig.org/download.html">SWIG for Windows (version 3+)</a></li>
             </ul>