Merge pull request #131 from molinch/master

Minor perf improvements and allow to get certificate information externally

Update dotAPNS to 4.2.1

Bump dotAPNS version to 4.2.0

Bump dotAPNS version to 4.1.0

Throw new ApnsCertificateExpiredException when SendAsync is called wi…

…th an expired APNs certificate

Bump dotAPNS version to 3.4.0