input: Write a python function to convert a string into a URL-friendly slug.
  assert slugify("This Is a Test") == "this-is-a-test"
  assert slugify(" Python    Programming ") == "python-programming"
  assert slugify("Make: IT   Simple") == "make:-it-simple"
output: def slugify(text):
      import re
      text = text.strip().lower()
      text = re.sub(r'\s+', '-', text)
      return text