mailmap: Change email address of Stefan Brankovic

Stefan Brankovic wants to use his new email address for his future
work in QEMU.

CC: Stefan Brankovic <stefan.brankovic@syrmia.com>
Signed-off-by: Aleksandar Markovic <aleksandar.qemu.devel@gmail.com>
Reviewed-by: Stefan Brankovic <stefan.brankovic@syrmia.com>
Message-Id: <20200602085215.12585-3-aleksandar.qemu.devel@gmail.com>

.mailmap

@@ -52,6 +52,7 @@ Paul Burton <pburton@wavecomp.com> <paul.burton@mips.com>
 Paul Burton <pburton@wavecomp.com> <paul.burton@imgtec.com>
 Paul Burton <pburton@wavecomp.com> <paul@archlinuxmips.org>
 Philippe Mathieu-Daudé <philmd@redhat.com> <f4bug@amsat.org>
+Stefan Brankovic <stefan.brankovic@syrmia.com> <stefan.brankovic@rt-rk.com.com>
 Yongbok Kim <yongbok.kim@mips.com> <yongbok.kim@imgtec.com>
 
 # Also list preferred name forms where people have changed their