make zshrc more non-osx friendly
make zshrc more non-osx friendly

Fix errors thrown when running zshrc on non-osx machines. Tested on a
Raspberry Pi.

nicknisi/dotfiles,ptgamr/dotfiles,jacobxk/dotfiles-1,Boukefalos/dotfiles,patnolanireland/dotfiles,OctavianRotari/dotfiles,fieteboerner/dotfiles,abhisood/dotfiles,Jooho/dotfiles_mac,damca/dotfiles-ubuntu,bbtb1982/dotfiles,paulhirschi/dotfiles,pekosi/dotfiles,OctavianRotari/dotfiles,ptgamr/dotfiles,zhenglaizhang/dotfiles-1,nicknisi/dotfiles,gblock0/dotfiles_unstable,fieteboerner/dotfiles,jbargu/dotfiles,nicknisi/dotfiles,joeandrews/dotfiles,neutrinog/dotfiles,zhenglaizhang/dotfiles-1,bbtb1982/dotfiles,fieteboerner/dotfiles,jacobxk/dotfiles-1,Jooho/dotfiles_mac,pekosi/dotfiles,dyong0/dotfiles,jbargu/dotfiles,patnolanireland/dotfiles,Reesi82/dotfiles,SlyDen/dotfiles,NerdPad/dotfiles,damca/dotfiles-ubuntu