d.wms: default format changed to png

git-svn-id: https://svn.osgeo.org/grass/grass/branches/releasebranch_7_0@63169 15284696-431f-4ddb-bdfa-cd5b030d7da7

gui/scripts/d.wms.py

@@ -59,7 +59,7 @@
 #% type: string
 #% description: Image format requested from the server
 #% options: geotiff,tiff,jpeg,gif,png,png8
-#% answer: geotiff
+#% answer: png
 #% guisection: Request
 #%end