Hardcoded certificate key in models/ApplePushModel.cpp

Hello, thank you for your work. It really saved our team a ton of time.

Sorry, for some reason I can't fork this project here to make a pull request (or push a branch for that matter) so I'll just describe the problem in this issue:

Apple push messages will not for anyone but project's author because in https://git.fairkom.net/chat/RocketChatMobilePushGateway/blob/master/models/ApplePushModel.cpp#L145 there is a hardcoded certificate key.

I've made a fork on github where I fixed this (and added timestamps to logs while I was at it), feel free to just apply commit https://github.com/q210/RocketChatMobilePushGateway/commit/a37074da74794efe53d197f763576579f81e0a9e

Edited Oct 05, 2018 by q210 Tim

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