input: Write a python function to score sentiment of a given text using a lexicon.
  assert score_sentiment('I am feeling happy', {'happy': 1, 'sad': -1, 'angry': -3}) == 0.4
  assert score_sentiment('I am very sad and angry', {'happy': 1, 'sad': -1, 'angry': -3}) == -1.33
  assert score_sentiment('Nothing really matters', {'happy': 1, 'sad': -1, 'angry': -3}) == 0.0
output: def score_sentiment(text, lexicon):
      words = text.split()
      sentiment_score = 0
      word_count = 0
      
      for word in words:
          if word in lexicon:
              sentiment_score += lexicon[word]
          word_count += 1
      
      if word_count == 0:
          return 0.0
      
      return round(sentiment_score / word_count, 2)