message: docker: install nightly before checking what version it is
diff: @@ -112,6 +112,7 @@ impl RustwideBuilder {
  fn detect_rustc_version(&self) -> Result<String> {
  info!("detecting rustc's version...");
  + self.toolchain.install(&self.workspace)?;
  let res = Command::new(&self.workspace, self.toolchain.rustc())
  .args(&["--version"])
  .log_output(false)
  