Update CI for python 3.8

- travis
  - switch to released version of 3.8
  - remove 3.8 from allowed_failures
- appveyor
  - add 3.8

Author: clbarnes

.travis.yml

@@ -13,10 +13,8 @@ matrix:
       env: FEATURES=python3
     - python: "3.7"
       env: FEATURES=python3
-    - python: "3.8-dev"
+    - python: "3.8"
       env: FEATURES=python3
-  allow_failures:
-    - python: "3.8-dev"
 
 env:
   global:

appveyor.yml

@@ -7,6 +7,8 @@ environment:
       FEATURES: python3
     - PYTHON: "C:/Python37-x64"
       FEATURES: python3
+    - PYTHON: "C:/Python38-x64"
+      FEATURES: python3
 
 install:
   - "SET PATH=%PYTHON%;%PYTHON%\\Scripts;%PATH%"