message: Remove wrong and unnecessary check for `build world`
  This was changed in to negate
  the condition (`!is_dir()` -> `is_dir()`), which is a bug. However, the
  whole check is unnecessary, `read_dir` already returns an error if the
  path isn't a directory.
diff: use crate::error::Result;
  -use anyhow::{ensure, Context};
  +use anyhow::Context;
  use serde_json::Value;
  use std::io::prelude::*;
  use std::io::BufReader;
  @@ -62,8 +62,6 @@ pub fn crates_from_path<F>(path: &Path, func: &mut F) -> Result<()>
  where
  F: FnMut(&str, &str),
  {
  - ensure!(!path.is_dir(), "Not a directory");
  -
  for file in path.read_dir()? {
  let file = file?;
  let path = file.path();
  