Fix appveyor config

Author: j4321

.appveyor.yml

@@ -5,6 +5,7 @@ environment:
     - PYTHON: "C:\\PYTHON35"
     - PYTHON: "C:\\PYTHON36"
 install:
+  - "%PYTHON%\\python.exe -m pip install -U pip"
   - "%PYTHON%\\python.exe -m pip install nose coverage codecov psutil pynput babel pillow pypiwin32"
 build: off
 test_script: