Fix compile error for libzmq 4.2.1 and 4.2.2 (#161)
Fix compile error for libzmq 4.2.1 and 4.2.2 (#161)

* Fix compile error for libzmq 4.2.1 and 4.2.2

When defined ZMQ_BUILD_DRAFT_API=1, you receive an error "'on_event_handshake_succeeded' was not declared in this scope"... which is correct for versions 4.2.1 and 4.2.2.
Function was renamed from 'on_event_handshake_succeed', fixed this by updating the function name.
zeromq/cppzmq,zeromq/cppzmq