maint: use dirs::home_dir() instead of deprecated std::env::home_dir()

[davvid]

cargo check warns that std::env::home_dir() is deprecated:

warning: use of deprecated item 'std::env::home_dir':
This function's behavior is unexpected and probably not
what you want. Consider using the home_dir function from
https://crates.io/crates/dirs instead.

Use dirs::home_dir() instead.

[whitequark]

Thanks!