update --exec python example to use print() syntax

git-svn-id: https://svn.osgeo.org/grass/grass/trunk@70020 15284696-431f-4ddb-bdfa-cd5b030d7da7

lib/init/grass7.html

@@ -349,15 +349,15 @@ import grass.script as gscript
 import grass.script.setup as gsetup
 
 gscript.message('Current GRASS GIS 7 environment:')
-print gscript.gisenv()
+print (gscript.gisenv())
  
 gscript.message('Available raster maps:')
 for raster in gscript.list_strings(type = 'raster'):
-    print raster
+    print (raster)
  
 gscript.message('Available vector maps:')
 for vector in gscript.list_strings(type = 'vector'):
-    print vector
+    print (vector)
 </pre></div>
 
 <h4>Troubleshooting</h4>