[licensing] python yolk license changed from GPLv2 to BSD

[Haïkel Guémar]

Hi,

i'm updating yolk from 0.4.1 to 0.4.3 which brings a license change:
GPLv2 to BSD.
The new license is the new BSD variant aka BSD 3 clauses (no
advertising) aka "kosher BSD" (compatible with GPLv2+)

According repoquery, no other packages requires it, just let me know if
it matters to you.

Best regards,
H.