Command Explorer EcludeFilter default should be empty array

[adilio]

Bug identified in Twitch Stream with @TylerLeonhardt .

https://github.com/PowerShell/vscode-powershell/blob/master/package.json#L508

Current Value:
"default":"",

Should Be:
"default":[""],
or
"default":[],

As referenced by @corbob