Fixed grammar in comment.

dlib/image_keypoint/hog_abstract.h

@@ -132,7 +132,7 @@ namespace dlib
         );
         /*!
             ensures
-                - copies all the state information of item into *this except for state 
+                - copies all the state information of item into *this, except for state 
                   information populated by load().  More precisely, given two hog_image 
                   objects H1 and H2, the following sequence of instructions should always 
                   result in both of them having the exact same state.