Connection leak due to HttpClient instantiation without an HttpClientFactory

[KeithHenry]

This line creates a HttpClient every time the service is created:

NeverBounceApi-DotNet/NeverBounceSDK/Utilities/HttpClientWrapper.cs

Line 43 in fa534a1

_client = new HttpClient();

This will cause more HTTP connections being opened, and left open as this connection isn't closed or disposed either.

This needs an HttpClientFactory to avoid the connection leak.

[KeithHenry]

This is fixed in our fork EvolutionJobs#3

#20 applies those changes back here.