[appveyor] errors are not errors

[GeoffWilliams]

Anything writing STDERR in appveyor shows up as an error, like this:

Entered PDQTest from C:/projects/puppet-windows-timezone/.pdqtest
bundle : pdk (INFO): Using Ruby 2.4.4
At C:\projects\puppet-windows-timezone\make.ps1:44 char:22
+         cd .pdqtest; bundle exec pdqtest all; cd ..
+                      ~~~~~~~~~~~~~~~~~~~~~~~
    + CategoryInfo          : NotSpecified: (pdk (INFO): Using Ruby 2.4.4:String) [], RemoteException
    + FullyQualifiedErrorId : NativeCommandError
 
pdk (INFO): Using Puppet 5.5.3

^^^ This is not an error!