input: Write a Python function to predict the sentiment of a given text using NLTK's VADER sentiment analysis tool.
  assert predict_sentiment("This is an amazing movie!") >= 0.5
  assert predict_sentiment("I hated this movie so much.") <= -0.5
  assert predict_sentiment("It was an okay film.") == 0.0
output: def predict_sentiment(text):
      from nltk.sentiment.vader import SentimentIntensityAnalyzer
      import nltk
      nltk.download('vader_lexicon')
      
      sia = SentimentIntensityAnalyzer()
      sentiment_scores = sia.polarity_scores(text)
      
      return sentiment_scores['compound']