add ws_key as get parameter as suggesed here: https://stackoverflow.c…

[gaboto83]

…om/questions/28749812/prestashop-web-service-api-keeps-asking-for-authentication

Questions	Answers
Description?	Please be specific when describing this change. What did you change? Why?
Type?	bug fix / improvement / new feature / refactor
BC breaks?	yes / no
Deprecations?	yes / no
Fixed ticket?	Fixes #{issue URL here}, Fixes #{another issue URL here}
Sponsor company	Your company or customer's name goes here (if applicable).
How to test?	Indicate how to verify that this change works as expected.

[ps-jarvis]

Hello @gaboto83!

This is your first pull request on PrestaShop-webservice-lib repository of the PrestaShop project.

Thank you, and welcome to this Open Source community!