plugins.md: replace memcached link
plugins.md: replace memcached link

With a better-maintained fork.
econya/dokku,jazzzz/dokku,netbrick/dokku,claytonbrown/dokku,codeconfab/dokku,dokku/dokku,codeconfab/dokku,amaltson/dokku,biddyweb/dokku,expa/dokku,biddyweb/dokku,crisward/dokku,pmvieira/dokku,fruitl00p/dokku,Cactusbone/dokku,crisward/dokku,econya/dokku,pmvieira/dokku,callahad/dokku,matto1990/dokku,u2mejc/dokku,TribeMedia/dokku,biddyweb/dokku,fmoliveira/dokku,vijayviji/dokku,elia/dokku,econya/dokku,johnfraney/dokku,expa/dokku,progrium/dokku,matto1990/dokku,claytonbrown/dokku,alessio/dokku,alessio/dokku,johnfraney/dokku,beedesk/dokku,bobvanderlinden/dokku,Evlos/dokku,u2mejc/dokku,AnselZhangGit/dokku,Evlos/dokku,fmoliveira/dokku,fruitl00p/dokku,crisward/dokku,mrluc/dokku,expa/dokku,sseemayer/dokku,mrluc/dokku,jimjag/dokku,pmvieira/dokku,jimjag/dokku,mrluc/dokku,vijayviji/dokku,eljojo/dokku,mrluc/dokku,vijayviji/dokku,u2mejc/dokku,Cactusbone/dokku,johnfraney/dokku,elia/dokku,davidsiefert/dokku,TribeMedia/dokku,dokku/dokku,Evlos/dokku,biddyweb/dokku,TribeMedia/dokku,codeconfab/dokku,alessio/dokku,codeconfab/dokku,callahad/dokku,eljojo/dokku,jimeh/dokku,jimeh/dokku,jazzzz/dokku,johnfraney/dokku,gianpaj/dokku,beedesk/dokku,alessio/dokku,codeconfab/dokku,jimeh/dokku,matto1990/dokku,gianpaj/dokku,econya/dokku,alexquick/dokku,progrium/dokku,expa/dokku,u2mejc/dokku,codeconfab/dokku,bobvanderlinden/dokku,matto1990/dokku,fmoliveira/dokku,fmoliveira/dokku,mouserage/dokku,bobvanderlinden/dokku,callahad/dokku,elia/dokku,dokku/dokku,progrium/dokku,AnselZhangGit/dokku,gianpaj/dokku,progrium/dokku,AnselZhangGit/dokku,crisward/dokku,u2mejc/dokku,gianpaj/dokku,progrium/dokku,dokku/dokku,mrluc/dokku,elia/dokku,jazzzz/dokku,netbrick/dokku,mrluc/dokku,callahad/dokku,progrium/dokku,fruitl00p/dokku,codeconfab/dokku,u2mejc/dokku,alexquick/dokku,jimjag/dokku,amaltson/dokku,pmvieira/dokku,alessio/dokku,netbrick/dokku,crisward/dokku,netbrick/dokku,matto1990/dokku,beedesk/dokku,TribeMedia/dokku,fruitl00p/dokku,eljojo/dokku,AnselZhangGit/dokku,jimeh/dokku,progrium/dokku,dokku/dokku,codeconfab/dokku,Evlos/dokku,alexquick/dokku,Cactusbone/dokku,eljojo/dokku,davidsiefert/dokku,TribeMedia/dokku,vijayviji/dokku,amaltson/dokku,amaltson/dokku,alexquick/dokku,sseemayer/dokku,bobvanderlinden/dokku,johnfraney/dokku,mouserage/dokku,vijayviji/dokku,johnfraney/dokku,claytonbrown/dokku,dokku/dokku,TribeMedia/dokku,netbrick/dokku,vijayviji/dokku,matto1990/dokku,jimjag/dokku,dokku/dokku,vijayviji/dokku,bobvanderlinden/dokku,biddyweb/dokku,biddyweb/dokku,claytonbrown/dokku,AnselZhangGit/dokku,mouserage/dokku,callahad/dokku,sseemayer/dokku,expa/dokku,jimeh/dokku,elia/dokku,gianpaj/dokku,jazzzz/dokku,jimjag/dokku,crisward/dokku,amaltson/dokku,eljojo/dokku,netbrick/dokku,bobvanderlinden/dokku,eljojo/dokku,callahad/dokku,beedesk/dokku,eljojo/dokku,sseemayer/dokku,expa/dokku,claytonbrown/dokku,matto1990/dokku,econya/dokku,jimjag/dokku,matto1990/dokku,AnselZhangGit/dokku,callahad/dokku,Evlos/dokku,sseemayer/dokku,Evlos/dokku,beedesk/dokku,mouserage/dokku,davidsiefert/dokku,davidsiefert/dokku,jimjag/dokku,johnfraney/dokku,fmoliveira/dokku,mrluc/dokku,gianpaj/dokku,bobvanderlinden/dokku,pmvieira/dokku,claytonbrown/dokku,amaltson/dokku,u2mejc/dokku,TribeMedia/dokku,sseemayer/dokku,callahad/dokku,sseemayer/dokku,claytonbrown/dokku,mouserage/dokku,davidsiefert/dokku,pmvieira/dokku,davidsiefert/dokku,pmvieira/dokku,fruitl00p/dokku,elia/dokku,Cactusbone/dokku,Cactusbone/dokku,AnselZhangGit/dokku,biddyweb/dokku,mouserage/dokku,Cactusbone/dokku,expa/dokku,expa/dokku,gianpaj/dokku,bobvanderlinden/dokku,beedesk/dokku,Cactusbone/dokku,alessio/dokku,alessio/dokku,fruitl00p/dokku,davidsiefert/dokku,jazzzz/dokku,Evlos/dokku,econya/dokku,beedesk/dokku,biddyweb/dokku,eljojo/dokku,jimjag/dokku,progrium/dokku,netbrick/dokku,dokku/dokku,beedesk/dokku,alexquick/dokku,jimeh/dokku,johnfraney/dokku,Evlos/dokku,crisward/dokku,AnselZhangGit/dokku,amaltson/dokku,fmoliveira/dokku,amaltson/dokku,fruitl00p/dokku,davidsiefert/dokku,jazzzz/dokku,mouserage/dokku,alessio/dokku,jimeh/dokku,netbrick/dokku,elia/dokku,econya/dokku,alexquick/dokku,econya/dokku,fruitl00p/dokku,sseemayer/dokku,jazzzz/dokku,elia/dokku,mouserage/dokku,fmoliveira/dokku,alexquick/dokku,Cactusbone/dokku,TribeMedia/dokku,crisward/dokku,jazzzz/dokku,mrluc/dokku,alexquick/dokku,u2mejc/dokku,fmoliveira/dokku,pmvieira/dokku,gianpaj/dokku,jimeh/dokku,vijayviji/dokku,claytonbrown/dokku