update to support python 3.6 (#117)

* update to support python 3.6

Author: anton-b

.travis.yml

@@ -9,6 +9,12 @@ jobs:
     python: 3.8
     install: pip install -U tox-travis
     script: tox
+  - python: 3.6
+    install: pip install -U tox-travis
+    script: tox
+  - python: 3.7
+    install: pip install -U tox-travis
+    script: tox
   - python: 3.8
     install:
       - pip install ./

setup.py

@@ -19,6 +19,7 @@
         'Intended Audience :: Developers',
         'License :: OSI Approved :: MIT License',
         'Natural Language :: English',
+        'Programming Language :: Python :: 3.6',
         'Programming Language :: Python :: 3.7',
         'Programming Language :: Python :: 3.8'
     ],

tox.ini

@@ -1,9 +1,11 @@
 [tox]
-envlist = py38
+envlist = py36, py37, py38
 
 [travis]
 python =
     3.8: py38
+    3.7: py37
+    3.6: py36
 
 [testenv]
 deps =