Fix mailmap for @gifnksm

cc rust-lang-nursery/thanks#71

.mailmap

@@ -132,9 +132,8 @@ Lindsey Kuper <lindsey@composition.al> <lkuper@mozilla.com>
 Luke Metz <luke.metz@students.olin.edu>
 Luqman Aden <me@luqman.ca> <laden@csclub.uwaterloo.ca>
 Luqman Aden <me@luqman.ca> <laden@mozilla.com>
-Makoto Nakashima <makoto.nksm+github@gmail.com> <makoto.nksm@gmail.com>
-Makoto Nakashima <makoto.nksm+github@gmail.com> gifnksm <makoto.nksm+github@gmail.com>
-Makoto Nakashima <makoto.nksm+github@gmail.com> NAKASHIMA, Makoto <makoto.nksm+github@gmail.com>
+NAKASHIMA, Makoto <makoto.nksm+github@gmail.com> <makoto.nksm@gmail.com>
+NAKASHIMA, Makoto <makoto.nksm+github@gmail.com> <makoto.nksm+github@gmail.com>
 Marcell Pardavi <marcell.pardavi@gmail.com>
 Margaret Meyerhofer <mmeyerho@andrew.cmu.edu> <mmeyerho@andrew>
 Mark Sinclair <mark.edward.x@gmail.com>
@@ -150,7 +149,6 @@ Michael Woerister <michaelwoerister@posteo> <michaelwoerister@gmail>
 Mickaël Raybaud-Roig <raybaudroigm@gmail.com> m-r-r <raybaudroigm@gmail.com>
 Ms2ger <ms2ger@gmail.com> <Ms2ger@gmail.com>
 Mukilan Thiagarajan <mukilanthiagarajan@gmail.com>
-NAKASHIMA, Makoto <makoto.nksm+github@gmail.com>
 Nathan Wilson <wilnathan@gmail.com>
 Nathaniel Herman <nherman@post.harvard.edu> Nathaniel Herman <nherman@college.harvard.edu>
 Neil Pankey <npankey@gmail.com> <neil@wire.im>