Update tox.ini

Removed 3.6 and 3.7 versions of python

Author: shankarpandala

tox.ini

@@ -1,13 +1,14 @@
 [tox]
-envlist = py36, py37, py38, py39 flake8
+envlist = py38, py39, py310, py311, py312, py313, flake8
 
 [travis]
 python =
     3.10: py310
+    3.11: py311
+    3.12: py312
+    3.13: py313
     3.9: py39
     3.8: py38
-    3.7: py37
-    3.6: py36
 
 [testenv:flake8]
 basepython = python