g,manual: fix import for python2 and python3

git-svn-id: https://svn.osgeo.org/grass/grass/trunk@68360 15284696-431f-4ddb-bdfa-cd5b030d7da7

scripts/g.manual/g.manual.py

@@ -50,7 +50,7 @@ import sys
 import os
 
 try:
-    from urlib import urlopen
+    from urllib2 import urlopen
 except ImportError:
     # python3
     from urllib.request import urlopen