mailmap: consolidate multiple addresses into one

Merges contributions made from three different addresses:

- win@wincent.com (old address, initial contributions in 2007–2009)
- greg@hurrell.net (personal address matching full name, so this one is
  the "forever" address; contributions made starting in 2018)
- greg.hurrell@datadoghq.com (current work address, used for recent
  contributions)

Signed-off-by: Greg Hurrell <greg.hurrell@datadoghq.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Author: wincent

.mailmap

@@ -81,6 +81,8 @@ Fredrik Kuivinen <frekui@gmail.com> <freku045@student.liu.se>
 Frédéric Heitzmann <frederic.heitzmann@gmail.com>
 Garry Dolley <gdolley@ucla.edu> <gdolley@arpnetworks.com>
 Glen Choo <glencbz@gmail.com> <chooglen@google.com>
+Greg Hurrell <greg@hurrell.net> <greg.hurrell@datadoghq.com>
+Greg Hurrell <greg@hurrell.net> <win@wincent.com>
 Greg Price <price@mit.edu> <price@MIT.EDU>
 Greg Price <price@mit.edu> <price@ksplice.com>
 Heiko Voigt <hvoigt@hvoigt.net> <git-list@hvoigt.net>