CreateStockAdjustment missing stock_location_id

[sambedingfield]

Hey! Thanks for the library.

Today I needed to use stock_location_id when creating a Stock Adjustment with CreateStockAdjustment, but it's not available.

Weirdly, it's also not documented at https://developer.tradegecko.com/docs.html?shell#create-a-new-stock_adjustment, however it does exist and works as intended when added. It's actually a required field when using the web interface, which is strange?

[bakura10]

Hi,

I would be happy to merge a change. Can you please submit a PR with the change? :)