Mailmap: Fix Christoph Rönsch.

(cherry picked from commit 8f45d2d)

Author: scottgonzalez

.mailmap

@@ -11,6 +11,7 @@ Ben Hollis <bhollis@amazon.com> <ben@benhollis.net>
 Benjamin Scott Boyle <benjamins.boyle@gmail.com>
 Bert ter Heide <bertjh@hotmail.com>
 Chairat Sunthornwiphat <pipo@sixhead.com>
+Christoph Rönsch <christoph.roensch@arcor.de>
 Corey Frang <gnarf37@gmail.com> <gnarf@gnarf.net>
 Courtland Allen <courtlandallen@gmail.com>
 Dan Streetman <ddstreet@ieee.org>