[bugfix] Allow subdomain to end with uppercase letter

[mhargrove]

Problem

reDomain regex currently returns ErrDomain errors for is.Domain on values that should be valid, ex. ABC.com

regex for subdomain values currently allows lower & upper case alpha-num for beginning and optional middle chars, but won't match if value is longer than one char and ends with upper case, ex. aBc.com is valid but abC.com returns ErrDomain

Reference

from https://github.com/go-ozzo/ozzo-validation/blob/master/is/rules.go#L246-L249:

// Domain regex source: https://stackoverflow.com/a/7933253
// Slightly modified: Removed 255 max length validation since Go regex does not
// support lookarounds. More info: https://stackoverflow.com/a/38935027
reDomain = regexp.MustCompile(`^(?:[a-zA-Z0-9](?:[a-zA-Z0-9-]{0,61}[a-z0-9])?\.)+(?:[a-zA-Z]{1,63}| xn--[a-z0-9]{1,59})$`)

Solution

updated to include uppercase letters in relevant part of the reDomain regex, which is in line with the stackoverflow answer already linked in the above referenced code comments

[mhargrove]

would we also want to add uppercase to the idn-label part, or should that be left as-is?

ex.

Suggested change

	reDomain = regexp.MustCompile(`^(?:[a-zA-Z0-9](?:[a-zA-Z0-9-]{0,61}[a-zA-Z0-9])?\.)+(?:[a-zA-Z]{1,63}| xn--[a-z0-9]{1,59})$`)
	reDomain = regexp.MustCompile(`^(?:[a-zA-Z0-9](?:[a-zA-Z0-9-]{0,61}[a-zA-Z0-9])?\.)+(?:[a-zA-Z]{1,63}| xn--[a-zA-Z0-9]{1,59})$`)