Minor clarification.

--HG--
extra : convert_revision : svn%3Afdd8eb12-d10e-0410-9acb-85c331704f74/trunk%403711

dlib/ref.h

@@ -15,7 +15,7 @@ namespace dlib
     {
         /*!
             WHAT THIS OBJECT REPRESENTS
-                This is a simple object that just contains a reference to another object. 
+                This is a simple object that just holds a reference to another object. 
                 It is useful because it can serve as a kind of "copyable reference".  
         !*/