input: Write a function to perform sentiment analysis on a given text using NLTK's SentimentIntensityAnalyzer.
  assert perform_sentiment_analysis("I love this place!")['compound'] > 0
  assert perform_sentiment_analysis("I hate this place!")['compound'] < 0
  assert perform_sentiment_analysis("This place is okay.")['compound'] == 0
output: def perform_sentiment_analysis(text):
      from nltk.sentiment.vader import SentimentIntensityAnalyzer
      sia = SentimentIntensityAnalyzer()
      return sia.polarity_scores(text)