input: Write a python function to analyze the sentiment score of a given text.
  assert sentiment_score('I love this product!')['pos'] > 0.5
  assert sentiment_score('I hate this so much!')['neg'] > 0.5
  assert sentiment_score('It is okay, not great but not bad either')['neu'] > 0.5
output: def sentiment_score(text):
      from nltk.sentiment import SentimentIntensityAnalyzer
      sia = SentimentIntensityAnalyzer()
      return sia.polarity_scores(text)