Use ConfigParser instead of SafeConfigParser in Python 3

The SafeConfigParser class has been renamed to ConfigParser in Python
3.2 [1]. The alias SafeConfigParser maybe removed in future versions of
Python 3. Use ConfigParser instead of SafeConfigParser in Python 3

[1] http://bugs.python.org/issue10627

Change-Id: I1403de0ccc554472333d6fa0fbb55cdc31dce05f
Closes-Bug: #1618666

doc/ext/support_matrix.py

@@ -128,8 +128,10 @@ class SupportMatrixDirective(rst.Directive):
 
         :returns: SupportMatrix instance
         """
-
-        cfg = configparser.SafeConfigParser()
+        if six.PY3:
+            cfg = configparser.ConfigParser()
+        else:
+            cfg = configparser.SafeConfigParser()
         env = self.state.document.settings.env
         fname = self.arguments[0]
         rel_fpath, fpath = env.relfn2path(fname)