Redirect stderr output from `npm ls -g` to /dev/null.
Redirect stderr output from `npm ls -g` to /dev/null.

Fixes #756.
devedbox/nvm,slariviere/nvm,hkdobrev/nvm,devedbox/nvm,owen-it/nvm,bbuck/nvm,jhliberty/nvm,cjac/nvm,cirosantilli/nvm,gtdeng/nvm,mmorejon/nvm,Ingelheim/nvm,Kuzirashi/nvm,pmq20/nvm,jbergstroem/nvm,ljharb/nvm,edwmurph/nvm,domenicosolazzo/nvm,gtdeng/nvm,DigitallySeamless/nvm,reybango/nvm,hanhailong/nvm,jaawerth/nvm,Theodeus/nvm,Theodeus/nvm,cnpm/nvm,lukechilds/nvm,jhliberty/nvm,icyflame/nvm,DigitallySeamless/nvm,SampleLiao/nvm,PeterDaveHello/nvm,psychoss/nvm,nontage24/nvm,joneit/nvm,bbuck/nvm,williamboman/nvm,joneit/nvm,domenicosolazzo/nvm,hanhailong/nvm,Kuzirashi/nvm,tianzhihen/nvm,egilkh/nvm,owen-it/nvm,greyhwndz/nvm,creationix/nvm,bevacqua/nvm,reybango/nvm,mmorejon/nvm,creationix/nvm,cirosantilli/nvm,PeterDaveHello/nvm,thomasf/nvm,mirydz/nvm,tlevine/nvm,JasonChrYoung/nvm,kmctown/nvm,tianzhihen/nvm,fnogatz/swivm,thomasf/nvm,williamboman/nvm,Richardphp/nvm,bevacqua/nvm,evocateur/nvm,lukechilds/nvm,slariviere/nvm,christophercaburog/nvm,kumaria/nvm,wahyutaufik/nvm,elrasguno/nvm,Richardphp/nvm,cjac/nvm,woss/nvm,woss/nvm,hkdobrev/nvm,Ingelheim/nvm,jaawerth/nvm,kmctown/nvm,wahyutaufik/nvm,dfackler/nvm,parasaro92/nvm,icyflame/nvm,JanChw/nvm,ljharb/nvm,youleiy/nvm,PeterDaveHelloKitchen/nvm,parasaro92/nvm,elrasguno/nvm,JasonChrYoung/nvm,kumaria/nvm,nontage24/nvm,psychoss/nvm,tlevine/nvm,christophercaburog/nvm,mirydz/nvm,youleiy/nvm,egilkh/nvm,dfackler/nvm,SampleLiao/nvm,PeterDaveHelloKitchen/nvm,edwmurph/nvm,cnpm/nvm,JanChw/nvm,jbergstroem/nvm,greyhwndz/nvm,pmq20/nvm,evocateur/nvm