update curl for 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
cc\ @briann