Upgrade to Python 3.8 for CI tests

.appveyor.yml

@@ -5,9 +5,9 @@ environment:
     - PYTHON: "C:\\Python27"
       PYTHON_VERSION: "2.7"
       TOXENV: "py27"
-    - PYTHON: "C:\\Python36"
-      PYTHON_VERSION: "3.6"
-      TOXENV: "py36"
+    - PYTHON: "C:\\Python38"
+      PYTHON_VERSION: "3.8"
+      TOXENV: "py38"
 
 init:
   - ECHO %PYTHON%

.travis.yml

@@ -12,13 +12,13 @@ matrix:
           os: linux
           python: 2.7
           env: TOXENV=py27
-        - name: "Run test suite on Linux with Python 3.6"
+        - name: "Run test suite on Linux with Python 3.8"
           os: linux
-          python: 3.6
-          env: TOXENV=py36
-        - name: "Check code style with pylama on Linux - Python 3.6"
+          python: 3.8
+          env: TOXENV=py38
+        - name: "Check code style with pylama on Linux - Python 3.8"
           os: linux
-          python: 3.6
+          python: 3.8
           env: TOXENV=pylama
           # 10.1 is OS X 10.13.x
           # https://docs.travis-ci.com/user/languages/objective-c/#Supported-OS-X-iOS-SDK-versions
@@ -28,9 +28,9 @@ matrix:
           language: generic
           python: 2.7
           env: TOXENV=py27
-        - name: "Run test suite on OS X with Python 3.6"
+        - name: "Run test suite on OS X with Python 3.8"
           os: osx
-          osx_image: xcode9.4
+          osx_image: xcode11
           language: generic
           env: TOXENV=py3