extend center line to arrow tip

git-svn-id: https://svn.osgeo.org/grass/grass/trunk@49353 15284696-431f-4ddb-bdfa-cd5b030d7da7

lib/symbol/symbol/extra/n_arrow3

@@ -35,7 +35,7 @@ END
 POLYGON
  RING
   LINE
-  0 3
+  0 7.5
   0 -7.5
  END
 END