Linuxbrew: Fix MacOS.version.from_symbol
Linuxbrew: Fix MacOS.version.from_symbol

Return 'linux' rather than nil

Closes #76

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