Fix typo in PSTypeName for Get-ServiceNowRequestItem

[replicaJunction]

I made an error in the output object's type name when submitting PR #61. This change corrects that behavior, so that Get-ServiceNowRequestItem correctly returns an object of type ServiceNow.RequestItem instead of ServiceNow.Request. Apologies for the inconvenience.

[Rick-2CA]

You had it as ServiceNow.RequestItem in your last PR. I changed it on you in order to have the formatting output the same as ServiceNow.Request. What I failed to remember was how all that worked. I should have expanded ServiceNow.format.ps1xml instead. My apologies for that error and thanks for reviewing the changes to catch me.