Modify the `kebabize` function so that it converts a camel case string into a kebab case.
Notes:
  - the returned string should only contain lowercase letters
import re
def kebabize(string):
    return re.sub(r'(?!^)([A-Z])', r'-\1', re.sub('\d', '', string)).lower()
import re
def kebabize(string):
    return re.sub(r'(?!^)([A-Z])', r'-\1', re.sub('\d', '', string)).lower()