Auto merge of #1761 - micbou:appveyor, r=puremourning

Fix AppVeyor configuration

AppVeyor certainly made some changes to their infrastructures because the `run_tests.py` script is not properly executed anymore. We now need to specifically call it with python.

This is already done in the `ycmd` repository so no changes needed there.

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appveyor.yml

@@ -11,6 +11,6 @@ install:
   - python C:\get-pip.py
   - pip install -r python\test_requirements.txt
 build_script:
-  - run_tests.py
+  - python run_tests.py
 # Disable automatic tests
 test: off