add update (PATCH)

[Edogusma]

Questions	Answers
Description?	add update (PATCH)
Type?	improvement
BC breaks?	no
Deprecations?	no
Fixed ticket?	no
Sponsor company	DrdLab
How to test?
$updatedXml = $this->webService->update([

        'resource' => 'products',
        'id'  => (int) $xml->product->id,
        'patchXml' => $xml->asXML(),

]);

[ps-jarvis]

Hello @Edogusma!

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

Thank you, and welcome to this Open Source community!

[gdebrion]

Please accept this PR