sec 13.3 (regexp): raw strings code is not shown

[murphyk]

In https://learningds.org/ch/13/text_regex.html you write Note that we add the r character before the quotes to create a raw string, which makes regexes easier to write. but the corresponding source code is not shown, so this statement is unclear.

show_regex_match(r'\d\d\d-\d\d-\d\d\d\d', 'My other number is 6382-13-38420.')