fixed a spelling error

--HG--
extra : convert_revision : svn%3Afdd8eb12-d10e-0410-9acb-85c331704f74/trunk%402458

dlib/svm/rbf_network_abstract.h

@@ -89,9 +89,9 @@ namespace dlib
         ) const
         /*!
             requires
-                - x == a matrix or something convertable to a matrix via vector_to_matrix().
+                - x == a matrix or something convertible to a matrix via vector_to_matrix().
                   Also, x should contain sample_type objects.
-                - y == a matrix or something convertable to a matrix via vector_to_matrix().
+                - y == a matrix or something convertible to a matrix via vector_to_matrix().
                   Also, y should contain scalar_type objects.
                 - x.nr() > 1
                 - x.nr() == y.nr() && x.nc() == 1 && y.nc() == 1