Update to Rust 2018 Edition.

lib/obj/Cargo.toml

@@ -8,6 +8,7 @@ repository = "https://github.com/CraneStation/wasmtime"
 categories = ["wasm"]
 license = "Apache-2.0 WITH LLVM-exception"
 readme = "README.md"
+edition = "2018"
 
 [dependencies]
 cranelift-codegen = "0.26.0"

lib/obj/src/lib.rs

@@ -26,11 +26,6 @@
     )
 )]
 
-extern crate cranelift_codegen;
-extern crate cranelift_entity;
-extern crate faerie;
-extern crate wasmtime_environ;
-
 mod emit_module;
 
-pub use emit_module::emit_module;
+pub use crate::emit_module::emit_module;