Update changelog for 8.1.2
Update changelog for 8.1.2

mParticle/mParticle-iOS-SDK,mParticle/mParticle-iOS-SDK,mParticle/mparticle-apple-sdk,mParticle/mParticle-iOS-SDK,mParticle/mparticle-apple-sdk,mParticle/mparticle-apple-sdk,mParticle/mparticle-apple-sdk,mParticle/mparticle-apple-sdk,mParticle/mparticle-apple-sdk