MetalPerformanceShaders macOS 11.0 Beta 4 to Beta 5 API Differences

../Frameworks/MPSNeuralNetwork.framework/Headers/MPSNNOptimizers.h
Added MPSNNOptimizerStochasticGradientDescent.useNesterovMomentum
Added -[MPSNNOptimizerStochasticGradientDescent initWithDevice:momentumScale:useNesterovMomentum:optimizerDescriptor:]