Incorrect domain validation

[StuBz211]

Incorrect domain validation since 2013 68ab79f
(spaces between 1 in regular expression- it's a first problem)

Code Version

7.5.0

Expected Behavior

Domain's validating success

Current Behavior

regexp doesn't work

Possible Solution

To update validation domain regexp

Steps to Reproduce

from saml2.validate import valid_domain_name

valid_domain_name('simple.domain.com')

and getting an error ValueError("Not a proper domain name")

[StuBz211]

Fix is coming folks!
#951