Install script breaks on nix-based installations

in a nix environment, the install script will try to download the binary into the nix store, which is a readonly file system.

Downloading https://github.com/subnut/nvim-ghost.nvim/releases/download/v0.5.4/
im-ghost-linux.tar.gz
#=#=#                                                                          
##O#- #                                                                        
Warning: Failed to open the file nvim-ghost-linux.tar.gz: Read-only file system
curl: (23) client returned ERROR on write of 16375 bytes


[Process exited 23]