Use impersonal language in German dpkg translation

Many thanks to Holger Wansing for his initial patch.

debian/changelog

@@ -16,7 +16,7 @@ dpkg (1.15.8.6) UNRELEASED; urgency=low
   * Spanish (Omar Campagne). Closes: #596519
 
   [ Updated programs translations ]
-  * German (Sven Joachim).
+  * German (Sven Joachim). Improved by Holger Wansing.
   * Portuguese (Miguel Figueiredo). Closes: #596168
   * Russian (Yuri Kozlov). Closes: #595455
   * Vietnamese (Clytie Siddall). Closes: #598473