input: Write a python function to find the word with the highest frequency in a dictionary.
  assert highest_freq_word({'python': 2, 'is': 1, 'an': 1, 'interpreted': 1, 'high-level': 1, 'general-purpose': 1, 'programming': 1, 'language': 1}) == 'python'
  assert highest_freq_word({'apple': 3, 'banana': 1, 'cherry': 2}) == 'apple'
  assert highest_freq_word({'dog': 1, 'cat': 1, 'bird': 1}) == 'dog'
output: def highest_freq_word(word_dict):
      return max(word_dict, key=word_dict.get)