[mailmap] Update my entry in the mailmap

Author: hamishknight

.mailmap

@@ -59,7 +59,8 @@ Graydon Hoare <ghoare@apple.com> <graydon@users.noreply.github.com>
 Greg Parker <gparker@apple.com> <gparker-github@sealiesoftware.com>
 Greg Titus <gregomni@gmail.com>
 Guillaume Lessard <dhtnstff@gmail.com> <glessard@users.noreply.github.com>
-Hamish <hamish2knight@gmail.com>
+Hamish Knight <hamish_knight@apple.com> <hamish2knight@gmail.com>
+Hamish Knight <hamish_knight@apple.com> <hamish_github@mediocremail.com>
 Han Sangjin <tinysun@jssolution.co.kr> <tinysun.net@gmail.com>
 Harlan Haskins <harlan@apple.com> <harlan@harlanhaskins.com>
 Harlan Haskins <harlan@apple.com> <hbh@google.com>