Don't allow adding the npm dir into the cache.
Don't allow adding the npm dir into the cache.

This prevents bundles from inadvertently installing themselves into
themselves making Exibit's head explode inside an explosion, dawg.

TimeToogo/npm,kimshinelove/naver-npm,segment-boneyard/npm,DIREKTSPEED-LTD/npm,cchamberlain/npm,ekmartin/npm,DaveEmmerson/npm,rsp/npm,chadnickbok/npm,cchamberlain/npm-msys2,ekmartin/npm,xalopp/npm,TimeToogo/npm,yibn2008/npm,cchamberlain/npm,chadnickbok/npm,DIREKTSPEED-LTD/npm,lxe/npm,kemitchell/npm,evocateur/npm,kriskowal/npm,haggholm/npm,Volune/npm,rsp/npm,thomblake/npm,thomblake/npm,yodeyer/npm,segment-boneyard/npm,misterbyrne/npm,segrey/npm,evocateur/npm,segment-boneyard/npm,kimshinelove/naver-npm,DIREKTSPEED-LTD/npm,segrey/npm,lxe/npm,Volune/npm,midniteio/npm,princeofdarkness76/npm,thomblake/npm,midniteio/npm,cchamberlain/npm-msys2,segrey/npm,DaveEmmerson/npm,princeofdarkness76/npm,kriskowal/npm,yyx990803/npm,ekmartin/npm,misterbyrne/npm,kemitchell/npm,yodeyer/npm,xalopp/npm,misterbyrne/npm,evanlucas/npm,kemitchell/npm,evanlucas/npm,segmentio/npm,segmentio/npm,haggholm/npm,chadnickbok/npm,yyx990803/npm,yibn2008/npm,TimeToogo/npm,evocateur/npm,lxe/npm,segmentio/npm,evanlucas/npm,kriskowal/npm,yyx990803/npm,rsp/npm,yodeyer/npm,haggholm/npm,midniteio/npm,kimshinelove/naver-npm,DaveEmmerson/npm,yibn2008/npm,cchamberlain/npm-msys2,cchamberlain/npm,xalopp/npm,princeofdarkness76/npm,Volune/npm