Update TravisCI build config

* The build is currently failing due to a known versioning issue with the "zipp" package on py27. Updating pip apparently fixes this
* Updated python 3 to "3.8" (from "3.6")

.travis.yml

@@ -4,10 +4,11 @@ language: python
 
 python:
   - "2.7"
-  - "3.6"
+  - "3.8"
 
 # command to install dependencies, e.g. pip install -r requirements.txt --use-mirrors
 install: 
+  - pip install -U pip
   - pip install -r requirements.txt
   - pip install coveralls