Fix broken YAML syntax

Author: dahlia

appveyor.yml

@@ -26,10 +26,10 @@ init:
 install:
 - git -C %PPVEYOR_BUILD_FOLDER% submodule update --init
 - ps: (new-object net.webclient).DownloadFile('https://bootstrap.pypa.io/get-pip.py', 'C:/get-pip.py')
-- %PYTHON%\python.exe C:/get-pip.py
-- %PYTHON%\Scripts\pip.exe --version
-- %PYTHON%\Scripts\pip.exe install wheel
-- %PYTHON%\Scripts\pip.exe install -e .
+- "%PYTHON%\\python.exe C:/get-pip.py"
+- "%PYTHON%\\Scripts\\pip.exe --version"
+- "%PYTHON%\\Scripts\\pip.exe install wheel"
+- "%PYTHON%\\Scripts\\pip.exe install -e ."
 build: false
 test_script:
 - "dir \"C:\\Program Files (x86)\""