Use math.gcd instead of fractions.gcd when possible

fractions.gcd() function has been removed from Python 3.9, it was deprecated since Python 3.5. https://docs.python.org/3.9/whatsnew/3.9.html#removed

Use math.gcd instead of fractions.gcd when possible
3c5de93c · Miro Hrončok · 4270277f · 3c5de93c
--- a/theano/tensor/nnet/abstract_conv.py
+++ b/theano/tensor/nnet/abstract_conv.py
@@ -6,7 +6,10 @@ from __future__ import absolute_import, print_function, division
 import logging
 from six import reraise, integer_types
 import sys
-from fractions import gcd
+try:
+    from math import gcd
+except ImportError:
+    from fractions import gcd

 import theano