update vendor docs to update inaccurate example

[satyapramodh]

Why

the example for pagerduty_service_integration within data.pagerduty_vendor had both type and vendor defined. This resulted in an error for me when i copied over the code and modified it for my usage.

Fix

As per service_integration docs, type cannot be used when vendor is defined. So in accordance to that, i modified the doc.

[stmcallister]

Good catch! Thank you! 👍 🎉