AdvancedUsage.md: ServerTrustPolicyManager -> ServerTrustManager (#3469)
AdvancedUsage.md: ServerTrustPolicyManager -> ServerTrustManager (#3469)

Replaced mentions of `ServerTrustPolicyManager` by `ServerTrustManager` in "Subclassing Server Trust Policy Manager" section.
Alamofire/Alamofire,yimajo/Alamofire,yimajo/Alamofire,Alamofire/Alamofire