Build: Add my new name to .mailmap, update it in AUTHORS.txt

Closes gh-1837

Author: mgol

.mailmap

@@ -78,6 +78,7 @@ Max Schnur <max.schnur@gmail.com>
 Michael Hollis <hollis21@gmail.com>
 Michael Stay <metaweta@gmail.com>
 Michael Wu <michaelmwu@gmail.com>
+Michał Gołębiowski-Owczarek <m.goleb@gmail.com>
 Mike Alsup <malsup@gmail.com>
 Milan Broum <midlis@googlemail.com>
 Mohamed Cherif Bouchelaghem <cherifbouchelaghem@yahoo.fr> <cherif@cherif.(none)>

AUTHORS.txt

@@ -312,7 +312,7 @@ Mani Mishra <manimishra902@gmail.com>
 Hannah Methvin <hannahmethvin@gmail.com>
 Leonardo Balter <leonardo.balter@gmail.com>
 Benjamin Albert <benjamin_a5@yahoo.com>
-Michał Gołębiowski <m.goleb@gmail.com>
+Michał Gołębiowski-Owczarek <m.goleb@gmail.com>
 Alyosha Pushak <alyosha.pushak@gmail.com>
 Fahad Ahmad <fahadahmad41@hotmail.com>
 Matt Brundage <github@mattbrundage.com>