input: Write a python function to create a Box class that initializes with height and width, and has a method to print the box using asterisks.
  assert Box(3, 4).print_box() == '****\n****\n****\n'
  assert Box(2, 2).print_box() == '**\n**\n'
  assert Box(1, 5).print_box() == '*****\n'
output: class Box:
      def __init__(self, height, width):
          self.height = height
          self.width = width
  
      def print_box(self):
          box = ('*' * self.width + '\n') * self.height
          return box