grass.desktop: add version number (trac https://trac.osgeo.org/grass/ticket/2777)

git-svn-id: https://svn.osgeo.org/grass/grass/branches/releasebranch_7_0@66866 15284696-431f-4ddb-bdfa-cd5b030d7da7

gui/icons/grass.desktop

@@ -48,6 +48,6 @@ Comment[uk]=Геоінформаційна система
 Comment[uz]=Geografik axborot tizimi
 Categories=Education;Science;Geoscience;Geography;
 Exec=grass70
-Icon=grass
+Icon=grass70
 Terminal=true
 Keywords=wms;wfs;ogc;osgeo;gis;