Fix the PK authenticated encryption example
Fix the PK authenticated encryption example

Spotted by @casevictor

blochberger/swift-sodium,blochberger/swift-sodium,ziogaschr/swift-sodium,ziogaschr/swift-sodium,jedisct1/swift-sodium,opfeffer/swift-sodium,ziogaschr/swift-sodium,opfeffer/swift-sodium,opfeffer/swift-sodium,jedisct1/swift-sodium,ziogaschr/swift-sodium,blochberger/swift-sodium,jedisct1/swift-sodium,opfeffer/swift-sodium,blochberger/swift-sodium