input: Write a function to crawl a website for specific data, in this case, phone numbers. The function takes a website URL as input, sends a request to get the webpage content, and then uses a regular expression to extract all phone numbers in the format '\d{3}-\d{3}-\d{4}' from the webpage content. If the webpage contains any phone numbers, the function will return them as a list, otherwise, it will return an empty list.
  
  assert crawl_website_for_phone_numbers('www.example.com')==['123-456-7890', '987-654-3210']
  assert crawl_website_for_phone_numbers('www.no_phone_numbers.com')==[]
  assert crawl_website_for_phone_numbers('www.invalid_url.com')==[]
output: import requests
  import re
  
  def crawl_website_for_phone_numbers(url):
      try:
          response = requests.get(f'http://{url}')
          response.raise_for_status()
          phone_numbers = re.findall(r'\d{3}-\d{3}-\d{4}', response.text)
          return phone_numbers
      except:
          return []