home: Use `xdg-open` on Linux and `open` on Mac OS
home: Use `xdg-open` on Linux and `open` on Mac OS

Closes homebrew/linuxbrew#28

rwhogg/brew,maxim-belkin/brew,rwhogg/brew,Linuxbrew/brew,rwhogg/brew,maxim-belkin/brew,hanxue/linuxbrew,hanxue/linuxbrew,hanxue/linuxbrew,Linuxbrew/brew,Linuxbrew/brew,Linuxbrew/brew,maxim-belkin/brew