mailmap: change primary address for Derrick Stolee

Stolee transitioned from Microsoft to GitHub in July 2020, but continued
to use <dstolee@microsoft.com> because it was a valid address. He also
used <stolee@gmail.com> to communicate with the mailing list since
writing plaintext emails is difficult in Outlook. However, recent issues
with GMail delaying mailing list messages created a need to change his
primary email address.

Signed-off-by: Derrick Stolee <derrickstolee@github.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

.mailmap

@@ -59,8 +59,9 @@ David Reiss <dreiss@facebook.com> <dreiss@dreiss-vmware.(none)>
 David S. Miller <davem@davemloft.net>
 David Turner <novalis@novalis.org> <dturner@twopensource.com>
 David Turner <novalis@novalis.org> <dturner@twosigma.com>
-Derrick Stolee <dstolee@microsoft.com> <stolee@gmail.com>
-Derrick Stolee <dstolee@microsoft.com> Derrick Stolee via GitGitGadget <gitgitgadget@gmail.com>
+Derrick Stolee <derrickstolee@github.com> <stolee@gmail.com>
+Derrick Stolee <derrickstolee@github.com> Derrick Stolee via GitGitGadget <gitgitgadget@gmail.com>
+Derrick Stolee <derrickstolee@github.com> <dstolee@microsoft.com>
 Deskin Miller <deskinm@umich.edu>
 Đoàn Trần Công Danh <congdanhqx@gmail.com> Doan Tran Cong Danh
 Dirk Süsserott <newsletter@dirk.my1.cc>