[examples] performance - port to rust 2018

examples/performance/Cargo.toml

@@ -2,6 +2,7 @@
 name = "performance"
 version = "0.1.0"
 authors = ["The wasm-bindgen Developers"]
+edition = "2018"
 
 [lib]
 crate-type = ["cdylib"]

examples/performance/src/lib.rs

@@ -1,7 +1,4 @@
-extern crate humantime;
-extern crate wasm_bindgen;
-extern crate web_sys;
-
+use humantime;
 use std::time::{Duration, SystemTime, UNIX_EPOCH};
 
 use wasm_bindgen::prelude::*;