message: Fix binaryen toolchain URL
diff: @@ -164,7 +164,7 @@ pub fn download_prebuilt(
  fn prebuilt_url(tool: &Tool, version: &str) -> Result<String, failure::Error> {
  let target = if target::LINUX && target::x86_64 {
  match tool {
  - Tool::WasmOpt => "x86-linux",
  + Tool::WasmOpt => "x86_64-linux",
  _ => "x86_64-unknown-linux-musl",
  }
  } else if target::LINUX && target::x86 {
  