npm update: document --dev flag (closes #6745)
npm update: document --dev flag (closes #6745)

Volune/npm,DaveEmmerson/npm,haggholm/npm,lxe/npm,kemitchell/npm,xalopp/npm,evocateur/npm,yibn2008/npm,haggholm/npm,evanlucas/npm,chadnickbok/npm,cchamberlain/npm-msys2,kimshinelove/naver-npm,cchamberlain/npm,cchamberlain/npm-msys2,ekmartin/npm,rsp/npm,yibn2008/npm,DIREKTSPEED-LTD/npm,midniteio/npm,princeofdarkness76/npm,haggholm/npm,misterbyrne/npm,midniteio/npm,evanlucas/npm,yodeyer/npm,DaveEmmerson/npm,lxe/npm,thomblake/npm,rsp/npm,TimeToogo/npm,chadnickbok/npm,cchamberlain/npm,rsp/npm,lxe/npm,xalopp/npm,princeofdarkness76/npm,cchamberlain/npm-msys2,cchamberlain/npm,princeofdarkness76/npm,yodeyer/npm,yibn2008/npm,yodeyer/npm,DIREKTSPEED-LTD/npm,kemitchell/npm,segrey/npm,ekmartin/npm,kemitchell/npm,TimeToogo/npm,kimshinelove/naver-npm,chadnickbok/npm,Volune/npm,thomblake/npm,misterbyrne/npm,kimshinelove/naver-npm,DaveEmmerson/npm,thomblake/npm,DIREKTSPEED-LTD/npm,Volune/npm,evocateur/npm,ekmartin/npm,evocateur/npm,segrey/npm,midniteio/npm,evanlucas/npm,xalopp/npm,segrey/npm,misterbyrne/npm,TimeToogo/npm