Fix call signature for local screenshot

[conorbranagan]

why

This function takes a set of kwargs rather than a dictionary, the call was failing.

what changed

• Pass through the payload as kwargs
• Added a test for this path
• Some whitespace was changed on save (I can remove this if this is an issue)

test plan

Added a new test for this and verified this locally in the work I'm doing using this library.

[conorbranagan]

Ah! I had missed #106, will close.