Update query doesn't have the correct arguments names for licence check

[nicolasprigent]

Hi @froger-me ,
Fantastic plugin, thanks a lot for this project !
I've found a bug in the integration examples. The correct query_args names for licence check while updating are 'update_license_key' and 'update_license_signature', not 'license_key' and 'license_signature'. After correcting this, my custom plugin can be updated correctly while having a valid licence.
I've made 2 Pull requests for plugin and theme examples.