Fix small typo in synopsis in npm-link.md.
Fix small typo in synopsis in npm-link.md.

Fix small typo (add 's') in command's synopsis in npm-link.md.
segrey/npm,kemitchell/npm,DaveEmmerson/npm,Volune/npm,DaveEmmerson/npm,xalopp/npm,xalopp/npm,princeofdarkness76/npm,lxe/npm,cchamberlain/npm,xalopp/npm,chadnickbok/npm,DIREKTSPEED-LTD/npm,thomblake/npm,yibn2008/npm,segrey/npm,lxe/npm,kemitchell/npm,rsp/npm,cchamberlain/npm-msys2,misterbyrne/npm,cchamberlain/npm-msys2,evanlucas/npm,rsp/npm,misterbyrne/npm,Volune/npm,ekmartin/npm,midniteio/npm,misterbyrne/npm,haggholm/npm,evocateur/npm,cchamberlain/npm-msys2,TimeToogo/npm,yodeyer/npm,yodeyer/npm,midniteio/npm,ekmartin/npm,midniteio/npm,lxe/npm,kimshinelove/naver-npm,yibn2008/npm,evocateur/npm,chadnickbok/npm,rsp/npm,evanlucas/npm,cchamberlain/npm,haggholm/npm,thomblake/npm,Volune/npm,cchamberlain/npm,thomblake/npm,kimshinelove/naver-npm,princeofdarkness76/npm,evanlucas/npm,DaveEmmerson/npm,TimeToogo/npm,DIREKTSPEED-LTD/npm,yibn2008/npm,TimeToogo/npm,segrey/npm,kemitchell/npm,DIREKTSPEED-LTD/npm,kimshinelove/naver-npm,yodeyer/npm,ekmartin/npm,haggholm/npm,chadnickbok/npm,princeofdarkness76/npm,evocateur/npm