Move module definitions after imports

The style guide says: "Put imports before module declarations."
See https://doc.rust-lang.org/style-guide/items.html

Cargo also does this automatically.

gdn/src/data.rs

@@ -1,13 +1,13 @@
-mod datadir;
-mod lockfile;
-mod v0;
-mod v1;
-
 use std::path::PathBuf;
 
 use anyhow::Context;
 use directories::ProjectDirs;
 
+mod datadir;
+mod lockfile;
+mod v0;
+mod v1;
+
 pub use self::{
     datadir::{LockedDataDir, UnlockedDataDir},
     v1::{VERSION, load_state, save_state},