update screenshot of graphical modeler in better quality

git-svn-id: https://svn.osgeo.org/grass/grass/trunk@64615 15284696-431f-4ddb-bdfa-cd5b030d7da7

gui/wxpython/gmodeler/g.gui.gmodeler.html

@@ -37,9 +37,9 @@ The Graphical Modeler allows you to:
 
 <center>
 <br>
-<img src="gmodeler_frame.jpg" border="1" alt="screenshot">
+<img src="gmodeler_frame.png">
 <br>
-Figure: A model to perform unsupervised classification using MLC and SMAP
+<i>Figure: A model to perform unsupervised classification using MLC and SMAP</i>
 </center>
 
 <h2>SEE ALSO</h2>