Sourcing /lib/async.zsh fails on nixOS

I just tried installing this theme on a nixOS install. When i run `zsh` I get:

`/home//.config/oh-my-zsh/themes/dracula.zsh-theme:source:16: no such file or directory: /nix/store/lib/async.zsh`

I think this is caused by `.zshrc` and `dracula.zsh-theme` being symlinks to a directory that's owned by root. `/nix/store` in this case.

I solved this by changing this line:

https://github.com/dracula/zsh/blob/master/dracula.zsh-theme#L16C1-L16C30

to:

`source ${ZSH_CUSTOM}/themes/lib/async.zsh
`

Start at line 16 of dracula.zsh-theme and reproduce the startup error on a NixOS installation by running zsh. Check how the theme resolves lib/async.zsh when the theme is symlinked into /nix/store. Done means the theme starts without the missing-file error and async.zsh is sourced from the expected location.

Written by the indexing model from the issue text.