upgrade pip

appveyor.yml

@@ -77,9 +77,6 @@ install:
   #- ECHO "Notepad location "
   #- ps: "ls C:\\Windows\\System32\\notepad.exe"
 
-  # Install zlib for pillow
-  - vcpkg install zlib
-
   # install the appropriate Miniconda (Py2/Py3, 32/64 bit),
   # as well as pywin32, pillow and coverage
   - "powershell ./ci/install.ps1"
@@ -89,6 +86,7 @@ install:
   # compiled extensions and are not provided as pre-built wheel packages,
   # pip will build them from source using the MSVC compiler matching the
   # target Python version and architecture
+  - "%CMD_IN_ENV% pip install --upgrade pip"
   - "%CMD_IN_ENV% pip install -r dev-requirements.txt"
   - "%CMD_IN_ENV% python -c \"import os,subprocess; os.environ.get('UIA_SUPPORT')=='YES' and subprocess.check_output(['pip','install','comtypes'])\""