Adds support for Py 3.8 (#65)

* adds py3.8 testing for travis [ch3350]
* updates requirements file for 3.8 compat

Author: looselycoupled

.travis.yml

@@ -5,6 +5,7 @@ dist: xenial
 python:
   - '3.6'
   - '3.7'
+  - '3.8'
 
 before_install:
   - sudo apt-get update

tests/requirements.txt

@@ -1,9 +1,9 @@
-pytest==4.0.2
-pytest-cov==2.6.0
+pytest==5.3.2
+pytest-cov==2.8.1
 pytest-flakes==4.0.0
-freezegun==0.3.11
+freezegun==0.3.12
 
 # dependencies for conversions
 numpy>=1.15
 pandas
-tabulate==0.8.3
+tabulate==0.8.6