Digest Auth issue due to _method not being set in PsychicRequest.cpp

[broddo]

Hi,

I spotted a bug in PsychicRequest.cpp which causes problems with Digest Auth:

https://github.com/hoeken/PsychicHttp/blob/58569481d5fc51d5fb07d2db2d0a081e3d899ed0/src/PsychicRequest.cpp#L427

_method is set to HTTP_GET in the initializer list but is never set anywhere else. This will cause digest auth to fail for any other method apart from GET.

The quick fix is to replace _method with a call to method()