chore: add Python 3.8 to Travis (#104)

Author: childish-sambino

.travis.yml

@@ -1,9 +1,12 @@
+dist: xenial # required for Python >= 3.7
 language: python
 python:
   - '2.7'
   - '3.4'
   - '3.5'
   - '3.6'
+  - '3.7'
+  - '3.8'
 install:
   - make install
   - make test-install
@@ -24,4 +27,4 @@ deploy:
     branch: master
     condition: "$TRAVIS_TEST_RESULT = 0"
     tags: true
-    python: "3.6"
+    python: '3.6'

README.rst

@@ -31,7 +31,7 @@ Installation
 Prerequisites
 -------------
 
--  Python version 2.7, 3.4, 3.5, or 3.6
+-  Python version 2.7 or 3.4+
 -  The SendGrid service, starting at the `free level`_
 
 Install Package