.mailmap: add an alias for Gert Wollny

Reviewed-by: Gert Wollny <gert.wollny@collabora.com>
diff --git a/.mailmap b/.mailmap
index cb8a27b..86b243e 100644
--- a/.mailmap
+++ b/.mailmap
@@ -175,6 +175,8 @@
 
 George Sapountzis <gsapountzis@gmail.com> George Sapountzis <gsap7@yahoo.gr>
 
+Gert Wollny <gert.wollny@collabora.com> <gw.fossdev@gmail.com>
+
 Gwenole Beauchesne <gwenole.beauchesne@intel.com> <gb.devel@gmail.com>
 
 Hamish Marson <hmarson@users.sourceforge.net> hmarson <hmarson>