boards/yunjia-nrf51822: fix broken links
boards/yunjia-nrf51822: fix broken links

yogo1212/RIOT,OTAkeys/RIOT,OlegHahm/RIOT,basilfx/RIOT,ant9000/RIOT,OlegHahm/RIOT,OTAkeys/RIOT,kYc0o/RIOT,basilfx/RIOT,authmillenon/RIOT,jasonatran/RIOT,RIOT-OS/RIOT,authmillenon/RIOT,RIOT-OS/RIOT,yogo1212/RIOT,ant9000/RIOT,RIOT-OS/RIOT,miri64/RIOT,yogo1212/RIOT,kYc0o/RIOT,ant9000/RIOT,basilfx/RIOT,yogo1212/RIOT,authmillenon/RIOT,kYc0o/RIOT,miri64/RIOT,kYc0o/RIOT,basilfx/RIOT,yogo1212/RIOT,OlegHahm/RIOT,kaspar030/RIOT,miri64/RIOT,jasonatran/RIOT,OTAkeys/RIOT,authmillenon/RIOT,kaspar030/RIOT,kaspar030/RIOT,jasonatran/RIOT,authmillenon/RIOT,RIOT-OS/RIOT,OTAkeys/RIOT,kYc0o/RIOT,authmillenon/RIOT,jasonatran/RIOT,RIOT-OS/RIOT,OlegHahm/RIOT,ant9000/RIOT,kaspar030/RIOT,OlegHahm/RIOT,OTAkeys/RIOT,jasonatran/RIOT,miri64/RIOT,kaspar030/RIOT,yogo1212/RIOT,basilfx/RIOT,ant9000/RIOT,miri64/RIOT