input: Write a python function to classify the sentiment of a given text using a predefined sentiment dictionary.
  assert sentiment_classifier("This is amazing!") == 'positive'
  assert sentiment_classifier("This is good.") == 'positive'
  assert sentiment_classifier("This is bad.") == 'negative'
  assert sentiment_classifier("This is awful!") == 'negative'
  assert sentiment_classifier("This is okay.") == 'neutral'
output: def sentiment_classifier(text):
      sentiment_dict = {
          'amazing': 'positive',
          'good': 'positive',
          'bad': 'negative',
          'awful': 'negative',
          'okay': 'neutral'
      }
      
      words = text.lower().split()
      
      for word in words:
          if word.strip(".,!?:;") in sentiment_dict:
              return sentiment_dict[word.strip(".,!?:;")]
      
      return 'neutral'