Add additional emails to .mailmap

Firefishy · Firefishy · commit 1aa8b8a761bf · 2019-12-08T15:46:10.000Z
diff --git a/.mailmap b/.mailmap
@@ -1,3 +1,3 @@
-Grant Slater <openstreetmap@firefishy.com> <git@firefishy.com>
+Grant Slater <openstreetmap@firefishy.com> <git@firefishy.com> <grant.slater@wearefriday.com> <github@firefishy.com>
 Guillaume Rischard <git@stereo.lu> <github@stereo.lu>
 Jochen Topf <jochen@topf.org> <jochen@remote.org>
