MFH: r469928

Update devel/py-pygit2 to 0.27.0 required by gitlab 10.7.x

Reviewed by: tz (mentor), wg (maintainer)
Approved by: tz (mentor), wg (maintainer)
Differential Revision: https://reviews.freebsd.org/D15319

Approved by: ports-secteam (eadler)