Update index.md

Author: JonathanMagnan

docs/index.md

@@ -116,7 +116,7 @@ layout: post
 								<a class="nav-link" href="https://github.com/zzzprojects/Eval-Expression.NET/issues" target="_blank">Forum</a>
 							</li>
 							<li class="nav-item">
-								<a class="nav-link" href="#pro">PRO Version</a>
+								<a class="nav-link" href="#pro">Buy</a>
 							</li>
 							<li class="nav-item">
 								<a href="https://www.nuget.org/packages/Z.Expressions.Eval/" target="_blank" class="btn btn-success" role="button" onclick="ga('send', 'event', { eventAction: 'download'});"><span><i class="fa fa-cloud-download"></i>&nbsp;<span>Download</span></span></a>