Bump python version

Bump tests version and supported versions in setup.py

stdlib: update packages for python 3.9

By utilizing the packages listed in
https://github.com/jackmaney/python-stdlib-list
for python 3.8 and 3.9, we were able to drop all stdlib packages that
existed solely in python 2 and add the missing stdlib python 3 packages

.travis.yml

@@ -4,17 +4,17 @@ language: python
 
 matrix:
   include:
+    - python: 3.9
+      env: TOX_ENV=py39
+    - python: 3.8
+      env: TOX_ENV=py38
+    - python: 3.7
+      env: TOX_ENV=py37
     - python: 3.6
       env: TOX_ENV=py36
-    - python: 3.5
-      env: TOX_ENV=py35
-    - python: 3.4
-      env: TOX_ENV=py34
-    - python: 2.7
-      env: TOX_ENV=py27
     - python: pypy3
       env: TOX_ENV=pypy3
-    - python: 3.6
+    - python: 3.9
       env: TOX_ENV=flake8
 
 # Use tox to run tests on Travis-CI to keep one unified method of running tests in any environment