input: Write a python function to plot a pie chart for the given responses dictionary using matplotlib.
  assert plot_pie_chart({'Apple': 30, 'Banana': 20, 'Cherry': 25, 'Date': 25}) == None
  assert plot_pie_chart({'Python': 45, 'JavaScript': 30, 'C++': 15, 'Java': 10}) == None
  assert plot_pie_chart({'Cat': 40, 'Dog': 30, 'Bird': 20, 'Fish': 10}) == None
output: def plot_pie_chart(responses):
      import matplotlib.pyplot as plt
  
      labels = responses.keys()
      sizes = responses.values()
  
      plt.figure(figsize=(8, 8))
      plt.pie(sizes, labels=labels, autopct='%1.1f%%', startangle=140)
      plt.axis('equal')  # Equal aspect ratio ensures that pie is drawn as a circle.
      plt.show()