fix cargo clippy error

shnmorimoto · shnmorimoto · commit b18488a9cacb · 2021-05-08T01:13:20.000+09:00
diff --git a/chapter2/src/2_4_6/main.rs b/chapter2/src/2_4_6/main.rs
@@ -1,5 +1,4 @@
 use chrono::Local;
-use serde_json;
 use serde_json::json;
 
 fn main() -> serde_json::Result<()> {
