icu4x-datagen --help is broken

[sffc]

Culprit is 737e9072b794685bd4ff9057273033b1821b44b5

How to reproduce: cargo run --all-features -p icu_datagen -- --help

Before the culprit, this outputted:

Learn more at: https://docs.rs/icu_datagen/1.4.1

Usage: icu4x-datagen [OPTIONS]

Options:
  -v, --verbose
          Requests verbose output
...

After the culprit:

error: unexpected argument found