$ cargo run
error: failed to get `trpl` as a dependency of package `async_await v0.1.0 (/Users/chris/dev/rust-lang/book/tmp/listings/ch17-async-await/listing-17-18)`

Caused by:
  failed to load source for dependency `trpl`

Caused by:
  Unable to update /Users/chris/dev/rust-lang/book/tmp/packages/trpl

Caused by:
  failed to read `/Users/chris/dev/rust-lang/book/tmp/packages/trpl/Cargo.toml`

Caused by:
  No such file or directory (os error 2)