message: Canonicalize default target if it ends with `.json`
diff: @@ -65,7 +65,17 @@ impl BuildConfig {
  failure::bail!("target was empty")
  }
  }
  - let cfg_target = config.get_string("build.target")?.map(|s| s.val);
  + let cfg_target = match config.get_string("build.target")? {
  + Some(ref target) if target.val.ends_with(".json") => {
  + let path = target.definition.root(config).join(&target.val);
  + let path_string = path
  + .into_os_string()
  + .into_string()
  + .map_err(|_| failure::format_err!("Target path is not valid unicode"));
  + Some(path_string?)
  + }
  + other => other.map(|t| t.val),
  + };
  let target = requested_target.or(cfg_target);
  if jobs == Some(0) {
  