input: Write a function to replace a specific pattern in a given text with a replacement string.
  assert replace_pattern("It was the best of times, it was the worst of times.", "times", "days") == "It was the best of days, it was the worst of days."
  assert replace_pattern("The quick brown fox jumps over the lazy dog", "fox", "cat") == "The quick brown cat jumps over the lazy dog"
  assert replace_pattern("Hello world, welcome to the universe.", "world", "planet") == "Hello planet, welcome to the universe."
output: def replace_pattern(text, pattern, replacement):
      return text.replace(pattern, replacement)