Suppress CLIXML output on Appveyor

[ianfixes]

System

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• URL of CI job: https://ci.appveyor.com/project/ianfixes/arduino-ci/build/1.0.34#L143
• URL of your Arduino project:

Issue Summary

There's an obscene amount of CLIXML text in the output.

#< CLIXML
System.Management.Automation.PSCustomObjectSystem.Object1Preparing modules for first use.0-1-1Completed-1 2Preparing modules for first use.0-1-1Completed-1 3Preparing modules for first use.0-1-1Completed-1 0Expand-Archive0-11Processing-1The archive file 'arduino-1.8.5' expansion is in progress...0Expand-Archive0-10Processing-1The archive file 'C:\projects\arduino-ci\arduino-1.8.5-windows.zip' expansion is in progress...0Expand-Archive0-10Processing-1The archive file 'C:\projects\arduino-ci\arduino-1.8.5-windows.zip' expansion is in progress...0Expand-Archive0-10Processing-1The archive file 'C:\projects\arduino-ci\arduino-1.8.5-windows.zip' expansion is in progress...0Expand-Archive0-10Processing-1The archive file 'C:\projects\arduino-ci\arduino-1.8.5-windows.zip' expansion

We should suppress it.