ignore py2.7 deprecation warning

Author: skvark

appveyor.yml

@@ -179,6 +179,7 @@ before_test:
 - ps: |
 
     cd ${Env:APPVEYOR_BUILD_FOLDER}\tests
+    $env:PYTHONWARNINGS = "ignore:::pip._internal.cli.base_command"
     &"${Env:PYTHON}/python.exe" -m pip install --user (ls "../dist/opencv_*.whl")
     if ($LastExitCode -ne 0) {throw $LastExitCode}