Migrate all crates to the 2018 edition

Most of the CLI crates were already in the 2018 edition, and it turns
out that one of the macro crates was already in the 2018 edition so we
may as well move everything to the 2018 edition!

Always nice to remove those `extern crate` statements nowadays!

This commit also does a `cargo fmt --all` to make sure we're conforming
with style again.

crates/web-sys/Cargo.toml

@@ -10,6 +10,7 @@ description = """
 Bindings for all Web APIs, a procedurally generated crate from WebIDL
 """
 license = "MIT/Apache-2.0"
+edition = "2018"
 
 [package.metadata.docs.rs]
 all-features = true

crates/web-sys/src/lib.rs

@@ -14,9 +14,6 @@
 #![doc(html_root_url = "https://docs.rs/web-sys/0.2")]
 #![allow(deprecated)]
 
-extern crate js_sys;
-extern crate wasm_bindgen;
-
 #[allow(unused_imports)]
 use js_sys::Object;
 

crates/web-sys/tests/wasm/whitelisted_immutable_slices.rs

@@ -12,7 +12,7 @@
 
 use wasm_bindgen::prelude::*;
 use wasm_bindgen_test::*;
-use web_sys::{WebGlRenderingContext, WebGl2RenderingContext};
+use web_sys::{WebGl2RenderingContext, WebGlRenderingContext};
 
 #[wasm_bindgen(module = "/tests/wasm/element.js")]
 extern "C" {