appveyor: work around wixtoolset missing checksum
appveyor: work around wixtoolset missing checksum

The wixtoolset package is currently broken on chocolatey but we can work
around it.

Signed-off-by: David Wagner <60228a510f9a76940848fa2d29321fc4edfc2119@intel.com>

01org/parameter-framework,01org/parameter-framework,dawagner/parameter-framework,01org/parameter-framework,dawagner/parameter-framework,dawagner/parameter-framework