Documentation: minor typo in proxy.md
Documentation: minor typo in proxy.md

This fixes a minor typo in proxy.md.

lorneli/etcd,shawnps/etcd,fasaxc/etcd,armstrongli/etcd,joshix/etcd,StorReduce/etcd,siddontang/etcd,fasaxc/etcd,jonboulle/etcd,ktateish/etcd,bluebreezecf/etcd,heyitsanthony/etcd,fanminshi/etcd,linuxcer/etcd,swingbach/etcd,visheshnp/etcd,insequent/etcd,tguangch/etcd,jlamillan/etcd,westhood/etcd,sofuture/etcd,glycerine/etcd,whuwxl/etcd,heyitsanthony/etcd,Timer/etcd,cockroachdb/etcd,wantonsolutions/dinv-etcd,tguangch/etcd,hongchaodeng/etcd,mqliang/etcd,etcd-io/etcd,dannysauer/etcd,tamird/etcd,a-robinson/etcd,achanda/etcd,hongchaodeng/etcd,westhood/etcd,bdarnell/etcd,OyTao/etcd_learning,ravigadde/etcd,yudai/etcd,dannysauer/etcd,shawnps/etcd,ravigadde/etcd,sayden/etcd,siddontang/etcd,mickep76/etcd,glevand/coreos--etcd,etcd-io/etcd,luxas/etcd,lorneli/etcd,raoofm/etcd,li-ang/etcd,vimalk78/etcd,zaphod-concur/etcd,li-ang/etcd,nekto0n/etcd,qqsun8819/etcd,ajityagaty/etcd,handsomesun/etcd,wantonsolutions/dinv-etcd,sayden/etcd,jonboulle/etcd,nekto0n/etcd,CrazyJvm/etcd,gyuho/etcd,akauppi/etcd,purpleidea/etcd,swingbach/etcd,cockroachdb/etcd,cchamplin/etcd,OyTao/etcd_learning,ajityagaty/etcd,bluebreezecf/etcd,coreos/etcd,YuleiXiao/etcd,rnaveiras/etcd,sebrandon1/etcd,lumjjb/etcd,plasticbox/etcd,sinsharat/etcd,purpleidea/etcd,endocode/etcd,rnaveiras/etcd,sebrandon1/etcd,chipironcin/etcd,raoofm/etcd,glycerine/etcd,joshix/etcd,StorReduce/etcd,xiang90/etcd,armstrongli/etcd,coreos/etcd,ktateish/etcd,whuwxl/etcd,tamird/etcd,sofuture/etcd,cchamplin/etcd,gyuho/etcd,mkumatag/etcd,glevand/coreos--etcd,xiang90/etcd,visheshnp/etcd,fasaxc/etcd,wantonsolutions/dinv-etcd,bdarnell/etcd,handsomesun/etcd,plasticbox/etcd,lumjjb/etcd,dnaeon/etcd,rchicoli/etcd,mickep76/etcd,endocode/etcd,yudai/etcd,vimalk78/etcd,Timer/etcd,luxas/etcd,linuxcer/etcd,jlamillan/etcd,insequent/etcd,rchicoli/etcd,ajityagaty/etcd,chipironcin/etcd,rnaveiras/etcd,mkumatag/etcd,etcd-io/etcd,CrazyJvm/etcd,YuleiXiao/etcd,mqliang/etcd,mqliang/etcd,a-robinson/etcd,qqsun8819/etcd,dnaeon/etcd,fanminshi/etcd,akauppi/etcd,mkumatag/etcd,sinsharat/etcd,achanda/etcd,zaphod-concur/etcd