Update curl to the latest version, 7.51.0 to get the latest security patches
curl 7.51.0 includes 11 security patches and we should update omnibus with the new release
- https://curl.haxx.se/docs/adv_20161102A.html
- https://curl.haxx.se/docs/adv_20161102B.html
- https://curl.haxx.se/docs/adv_20161102K.html
- https://curl.haxx.se/docs/adv_20161102J.html
- https://curl.haxx.se/docs/adv_20161102I.html
- https://curl.haxx.se/docs/adv_20161102H.html
- https://curl.haxx.se/docs/adv_20161102G.html
- https://curl.haxx.se/docs/adv_20161102F.html
- https://curl.haxx.se/docs/adv_20161102E.html
- https://curl.haxx.se/docs/adv_20161102D.html
- https://curl.haxx.se/docs/adv_20161102C.html
Fixes https://gitlab.com/gitlab-org/omnibus-gitlab/issues/1681