fsprobe: change latency precision .2 -> .4

Summary: File access latency can actually be less then 1 ms, so it's good to show more digits

Reviewed By: DurhamG

Differential Revision: D30942905

fbshipit-source-id: 2fc8d48dbc08c55b89d829d1474ae11c2c3df1c3

eden/scm/exec/fsprobe/src/main.rs

@@ -41,7 +41,7 @@ fn main() {
     let lat = duration_ms / files;
     let qps = files / duration_ms;
     println!(
-        "lat: {:.2} ms, qps: {:.0}, dur: {:?}, {}, rate {}",
+        "lat: {:.4} ms, qps: {:.0}, dur: {:?}, {}, rate {}",
         lat, qps, duration, stats, rate
     );
 }