Fix PowerShell errors on stderr

PS invocation of code coverage upload gets triggered because of stderr
output from curl with progress report when uploading coverage.

appveyor.yml

@@ -15,8 +15,8 @@ test_script:
   - ps: if ($env:APPVEYOR_BUILD_WORKER_IMAGE -eq "Visual Studio 2015") { .\tests\autotest-appveyor.ps1 9 10 11 12 14 }
   - ps: if ($env:APPVEYOR_BUILD_WORKER_IMAGE -eq "Visual Studio 2017") { .\tests\autotest-appveyor.ps1 15 }
   - ps: if ($env:APPVEYOR_BUILD_WORKER_IMAGE -eq "Visual Studio 2019") { .\tests\autotest-appveyor.ps1 19 }
-  - ps: if ($env:APPVEYOR_BUILD_WORKER_IMAGE -eq "Visual Studio 2015") { & C:\cygwin\bin\bash.exe -c "PATH=/usr/bin:/usr/local/bin:$PATH; make config=coverage test && bash <(curl -s https://codecov.io/bash) -f pugixml.cpp.gcov" }
-  - ps: if ($env:APPVEYOR_BUILD_WORKER_IMAGE -eq "Visual Studio 2015") { & C:\cygwin\bin\bash.exe -c "PATH=/usr/bin:/usr/local/bin:$PATH; make config=coverage defines=PUGIXML_WCHAR_MODE test && bash <(curl -s https://codecov.io/bash) -f pugixml.cpp.gcov" }
+  - ps: if ($env:APPVEYOR_BUILD_WORKER_IMAGE -eq "Visual Studio 2015") { & C:\cygwin\bin\bash.exe -c "PATH=/usr/bin:/usr/local/bin:$PATH; make config=coverage test && bash <(curl -s https://codecov.io/bash) -f pugixml.cpp.gcov 2>&1" }
+  - ps: if ($env:APPVEYOR_BUILD_WORKER_IMAGE -eq "Visual Studio 2015") { & C:\cygwin\bin\bash.exe -c "PATH=/usr/bin:/usr/local/bin:$PATH; make config=coverage defines=PUGIXML_WCHAR_MODE test && bash <(curl -s https://codecov.io/bash) -f pugixml.cpp.gcov 2>&1" }
 
 artifacts:
   - path: .\scripts\*.nupkg