When the root cache is not writable use home_cache
When the root cache is not writable use home_cache

The home_cache is `~/Library/Caches/Homebrew` on MacOS and
`~/.cache/Homebrew` on other systems.
Closes Homebrew/linuxbrew#17.

winordie-47/linuxbrew1,tomas/linuxbrew,danabrand/linuxbrew,afdnlw/linuxbrew,gcstang/linuxbrew,saketkc/linuxbrew,ebouaziz/linuxbrew,bukzor/linuxbrew,oneillkza/linuxbrew,hyokosdeveloper/linuxbrew,dholm/linuxbrew,DoomHammer/linuxbrew,tdsmith/linuxbrew,gnubila-france/linuxbrew,outcoldman/linuxbrew,brevilo/linuxbrew,hyokosdeveloper/linuxbrew,amenk/linuxbrew,gcstang/linuxbrew,jbaum98/linuxbrew,arcivanov/linuxbrew,digiter/linuxbrew,caputomarcos/linuxbrew,jwillemsen/linuxbrew,IsmailM/linuxbrew,Gui13/linuxbrew,Angeldude/linuxbrew,outcoldman/linuxbrew,telamonian/linuxbrew,princeofdarkness76/linuxbrew,iggyvolz/linuxbrew,telamonian/linuxbrew,digiter/linuxbrew,cbeck88/linuxbrew,tbetbetbe/linuxbrew,tomas/linuxbrew,caputomarcos/linuxbrew,Angeldude/linuxbrew,tghs/linuxbrew,10sr/linuxbrew,reelsense/linuxbrew,princeofdarkness76/linuxbrew,lvicentesanchez/linuxbrew,cbeck88/linuxbrew,afdnlw/linuxbrew,arcivanov/linuxbrew,jack-and-rozz/linuxbrew,drbenmorgan/linuxbrew,sublimino/linuxbrew,bukzor/linuxbrew,amenk/linuxbrew,SuperNEMO-DBD/cadfaelbrew,tjhei/linuxbrew,Angeldude/linuxbrew,ebouaziz/linuxbrew,princeofdarkness76/linuxbrew,jlisic/linuxbrew,jlisic/linuxbrew,DoomHammer/linuxbrew,drbenmorgan/linuxbrew,LeonB/linuxbrew,davydden/linuxbrew,tghs/linuxbrew,Linuxbrew/linuxbrew,dunn/linuxbrew,10sr/linuxbrew,sarvex/linuxbrew,tjhei/linuxbrew,SuperNEMO-DBD/cadfaelbrew,IsmailM/linuxbrew,jbaum98/linuxbrew,tjhei/linuxbrew,afdnlw/linuxbrew,brendanator/linuxbrew,gnubila-france/linuxbrew,drbenmorgan/linuxbrew,gnubila-france/linuxbrew,Gui13/linuxbrew,sarvex/linuxbrew,hyokosdeveloper/linuxbrew,gnubila-france/linuxbrew,sjackman/linuxbrew,Linuxbrew/linuxbrew,jlisic/linuxbrew,dunn/linuxbrew,oneillkza/linuxbrew,digiter/linuxbrew,Homebrew/linuxbrew,davydden/linuxbrew,sjackman/linuxbrew,davydden/linuxbrew,SuperNEMO-DBD/cadfaelbrew,Angeldude/linuxbrew,tbetbetbe/linuxbrew,telamonian/linuxbrew,romejoe/linuxbrew,reelsense/linuxbrew,IsmailM/linuxbrew,10sr/linuxbrew,amenk/linuxbrew,bukzor/linuxbrew,tbetbetbe/linuxbrew,jbaum98/linuxbrew,davydden/linuxbrew,dholm/linuxbrew,saketkc/linuxbrew,adamliter/linuxbrew,sjackman/linuxbrew,tghs/linuxbrew,jbaum98/linuxbrew,trskop/linuxbrew,brevilo/linuxbrew,adamliter/linuxbrew,tghs/linuxbrew,outcoldman/linuxbrew,lvicentesanchez/linuxbrew,brevilo/linuxbrew,sjackman/linuxbrew,reelsense/linuxbrew,LeonB/linuxbrew,dholm/linuxbrew,danabrand/linuxbrew,adamliter/linuxbrew,winordie-47/linuxbrew1,trskop/linuxbrew,digiter/linuxbrew,Homebrew/linuxbrew,ebouaziz/linuxbrew,dunn/linuxbrew,romejoe/linuxbrew,Homebrew/linuxbrew,gcstang/linuxbrew,tdsmith/linuxbrew,danabrand/linuxbrew,reelsense/linuxbrew,ebouaziz/linuxbrew,caputomarcos/linuxbrew,romejoe/linuxbrew,sarvex/linuxbrew,brendanator/linuxbrew,arcivanov/linuxbrew,afdnlw/linuxbrew,DoomHammer/linuxbrew,jwillemsen/linuxbrew,lvicentesanchez/linuxbrew,Gui13/linuxbrew,iggyvolz/linuxbrew,tbetbetbe/linuxbrew,caputomarcos/linuxbrew,tdsmith/linuxbrew,sublimino/linuxbrew,cbeck88/linuxbrew,saketkc/linuxbrew,winordie-47/linuxbrew1,danabrand/linuxbrew,oneillkza/linuxbrew,tomas/linuxbrew,tdsmith/linuxbrew,lvicentesanchez/linuxbrew,SuperNEMO-DBD/cadfaelbrew,LeonB/linuxbrew,sublimino/linuxbrew,jack-and-rozz/linuxbrew,adamliter/linuxbrew,drbenmorgan/linuxbrew,saketkc/linuxbrew,DoomHammer/linuxbrew,amenk/linuxbrew,digiter/linuxbrew,Linuxbrew/linuxbrew,Gui13/linuxbrew,iggyvolz/linuxbrew,tghs/linuxbrew,IsmailM/linuxbrew,winordie-47/linuxbrew1,jack-and-rozz/linuxbrew,sublimino/linuxbrew,bukzor/linuxbrew,tomas/linuxbrew,brendanator/linuxbrew,jwillemsen/linuxbrew,trskop/linuxbrew,oneillkza/linuxbrew,Homebrew/linuxbrew,Gui13/linuxbrew,hyokosdeveloper/linuxbrew,tdsmith/linuxbrew,Linuxbrew/linuxbrew,sarvex/linuxbrew,dunn/linuxbrew