input: Write a python function to import TensorFlow and create a simple neural network with one hidden layer.
  assert type(create_neural_network().layers[1].__class__.__name__) == str
  assert create_neural_network().layers[0].input_shape == (None, 784)
  assert create_neural_network().layers[1].output_shape == (None, 128)
output: def create_neural_network():
      import tensorflow as tf
      from tensorflow.keras.models import Sequential
      from tensorflow.keras.layers import Dense
      
      model = Sequential()
      model.add(Dense(784, input_shape=(784,)))
      model.add(Dense(128, activation='relu'))
      model.add(Dense(10, activation='softmax'))
      
      return model