examples/ndn-ping: fix typos
examples/ndn-ping: fix typos

OlegHahm/RIOT,OTAkeys/RIOT,RIOT-OS/RIOT,mtausig/RIOT,authmillenon/RIOT,jasonatran/RIOT,jasonatran/RIOT,authmillenon/RIOT,jasonatran/RIOT,x3ro/RIOT,authmillenon/RIOT,authmillenon/RIOT,kaspar030/RIOT,x3ro/RIOT,ant9000/RIOT,RIOT-OS/RIOT,josephnoir/RIOT,mtausig/RIOT,OlegHahm/RIOT,kaspar030/RIOT,miri64/RIOT,RIOT-OS/RIOT,kYc0o/RIOT,OTAkeys/RIOT,smlng/RIOT,aeneby/RIOT,smlng/RIOT,OlegHahm/RIOT,x3ro/RIOT,aeneby/RIOT,jasonatran/RIOT,aeneby/RIOT,OTAkeys/RIOT,smlng/RIOT,toonst/RIOT,aeneby/RIOT,miri64/RIOT,kYc0o/RIOT,jasonatran/RIOT,miri64/RIOT,basilfx/RIOT,kYc0o/RIOT,ant9000/RIOT,ant9000/RIOT,yogo1212/RIOT,yogo1212/RIOT,basilfx/RIOT,authmillenon/RIOT,josephnoir/RIOT,josephnoir/RIOT,josephnoir/RIOT,OlegHahm/RIOT,kaspar030/RIOT,yogo1212/RIOT,smlng/RIOT,miri64/RIOT,miri64/RIOT,authmillenon/RIOT,ant9000/RIOT,mtausig/RIOT,basilfx/RIOT,ant9000/RIOT,x3ro/RIOT,RIOT-OS/RIOT,basilfx/RIOT,x3ro/RIOT,yogo1212/RIOT,toonst/RIOT,OTAkeys/RIOT,kaspar030/RIOT,toonst/RIOT,toonst/RIOT,yogo1212/RIOT,basilfx/RIOT,OlegHahm/RIOT,aeneby/RIOT,OTAkeys/RIOT,toonst/RIOT,kYc0o/RIOT,yogo1212/RIOT,kYc0o/RIOT,josephnoir/RIOT,smlng/RIOT,mtausig/RIOT,mtausig/RIOT,kaspar030/RIOT,RIOT-OS/RIOT