Using [NSBundle bundleForClass:[self class]]
is dangerous because the code will behave differently depending on how AFNetworking is integrated.
If it is integrated as a static library (for example using CocoaPods), certificates will be searched in the main bundle.
If it is integrated as a framework (for example using Carthage), certificates will be searched in the AFNetworking framework.
Even though this behavior is documented, this is dangerous. Using the main bundle makes the behavior deterministic.
Fixes #3575