Update Request/PR: Amazon PA API 5.0

[jvv8]

PA API 4 will sunset on October 31st 2019.
Upgrade to PA API 5.0 is necessary in order for the package to function after said date.
Anyone working on this currently?

[michalbundyra]

@jvv8 we are working on migration to Laminas and we have made decision that this library is not going to be supported and moved to Laminas. We are suggesting to use https://github.com/aws/aws-sdk-php instead, as it the official library.