Update credits file

CREDITS

 The following core developers work or have been working on the Open eCard Client:
  - Benedikt Biallowons <benedikt.biallowons@ecsec.de>
+ - Daniel Nemmert <daniel.nemmert@ecsec.de>
  - Dirk Petrautzki <petrautzki@hs-coburg.de>
  - Johannes Schmölz <johannes.schmoelz@ecsec.de>
  - Moritz Horsch <moritz.horsch@ecsec.de>
  - Sebastian Lösch <slo@bos-bremen.de>
  - Simon Potzernheim <potzernheim@hs-coburg.de>
  - Tobias Wich <tobias.wich@ecsec.de>
+ - Wael Alkhatib <walkhatib@cdc.informatik.tu-darmstadt.de>
 
 
 The following developers contributed to the Open eCard Client: