Update memberships.wml to remove Desktop Linux Consortium and add Open Source Initiative. (!44) · Merge requests · Debian Webmaster Team / webwml

Removed Desktop Linux Consotrium, as organization no longer exists (https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=861781#5).
Added Open Source Initiative, which is included on the list of affiliates on the OSI web page (https://opensource.org/affiliates/list and https://www.debian.org/News/2012/20120330).

Update memberships.wml to remove Desktop Linux Consortium and add Open Source Initiative.