Correct typo.

Author: tonyg

tools/README

@@ -1,6 +1,6 @@
 This directory contains third-party tools that are used in the build
 of the software or its documentation, but that are not part of the
-software or its documentation. Each tools has its own copyright and
+software or its documentation. Each tool has its own copyright and
 software license, and is unaffected by the copyright and licensing of
 the RabbitMQ .NET client library.