fix typo

git-svn-id: https://svn.apache.org/repos/asf/ant/core/trunk@274172 13f79535-47bb-0310-9956-ffa450edef68

docs/manual/CoreTasks/exec.html

@@ -14,7 +14,7 @@ the command is only executed when Ant is run on one of the specified operating
 systems.</p>
 
 <h4>Cygwin Users</h4>
-<p>In general the &lt;exec&gt; task will not userstand paths such as /bin/sh for 
+<p>In general the &lt;exec&gt; task will not understand paths such as /bin/sh for 
 the executable parameter. This is because the Java VM in which Ant is running is a 
 Windows executable and is not aware of Cygwin conventions.
 </p>