changed slightly to avoid a warning in visual studio

--HG--
extra : convert_revision : svn%3Afdd8eb12-d10e-0410-9acb-85c331704f74/trunk%402494

dlib/test/matrix.cpp

@@ -1414,7 +1414,7 @@ namespace
             // make sure the multiply optimizations aren't messing things up
             DLIB_CASSERT(trans(i)*i == tmp(trans(i)*i),"");
             DLIB_CASSERT(equal(trans(a)*a , tmp(trans(a)*a), 1e-11),max(abs(trans(a)*a - tmp(trans(a)*a))));
-            DLIB_CASSERT(equal(trans(b)*b , tmp(trans(b)*b), 1e-3),max(abs(trans(b)*b - tmp(trans(b)*b))));
+            DLIB_CASSERT(equal(trans(b)*b , tmp(trans(b)*b), 1e-3f),max(abs(trans(b)*b - tmp(trans(b)*b))));
         }
 
     }