[MNT] - Add python 3.9 testing (#188)

* add python 3.9 testing
* list 3.9 support

Author: TomDonoghue

.travis.yml

@@ -5,6 +5,7 @@ python:
   - "3.6"
   - "3.7"
   - "3.8"
+  - "3.9"
 
 install:
   - pip install -r requirements.txt

setup.py

@@ -41,7 +41,8 @@
         'Programming Language :: Python :: 3.5',
         'Programming Language :: Python :: 3.6',
         'Programming Language :: Python :: 3.7',
-        'Programming Language :: Python :: 3.8'
+        'Programming Language :: Python :: 3.8',
+        'Programming Language :: Python :: 3.9'
     ],
     platforms = 'any',
     project_urls = {