Build problem on NetBSD

We've packaged sequoia-sq for NetBSD (pkgsrc) and had one build problem in this crate. The stat nanosecond member has a different name (depending on the operating system).

The patch we came up with for 0.3.1 is:

@@ -69,7 +69,7 @@ impl Metadata {
     pub fn modified(&self) -> std::time::Duration {
         std::time::Duration::new(
             self.0.st_mtime as u64,
-            self.0.st_mtime_nsec as u32)
+            self.0.st_mtimensec as u32)
     }

     /// Whether a file is a directory.

but I don't know what the proper way to do this is.