Fix: 'libraries and tool' to 'libraries and tools'

Author: lknknm

clang/www/features.html

@@ -156,7 +156,7 @@ <h3><a name="libraryarch">Library Based Architecture</a></h3>
 any specific client."</p></blockquote>
 
 <p>
-Currently, clang is divided into the following libraries and tool:
+Currently, clang is divided into the following libraries and tools:
 </p>
 
 <ul>