input: Write a python function to convert a string to title case.
  assert to_title_case("hello world") == "Hello World"
  assert to_title_case("convert this string") == "Convert This String"
  assert to_title_case("PYTHON is awesome") == "Python Is Awesome"
  assert to_title_case("123 abc DEF") == "123 Abc Def"
output: def to_title_case(s):
      return s.title()