Fix SyntaxWarning in setup.py

[Dobatymo]

Newer python versions raise a syntax warning when installing dlib.

<string>:235: SyntaxWarning: invalid escape sequence '\('
<string>:236: SyntaxWarning: invalid escape sequence '\('
<string>:237: SyntaxWarning: invalid escape sequence '\('

[davisking]

Thanks for the PR :)

[debnil-mercor]

Ran into this error earlier. Could a release be cut that includes this commit?

Thank you so much for all the hard work in maintenance! :)

[debnil-mercor]

Quick bump to the above - a new release with this commit would really be appreciated and fix breaking changes! @davisking

[davisking]

Oops, yeah, sorry for the delay. Just updated it.