Panic when --target-dir is supplied

[tomasol]

🐛 Bug description

Running the latest (48177dc) wasm-pack panics if --target-dir is supplied (and arguments are not sorted )

wasm-pack build --no-typescript --target bundler --out-dir build --dev --target-dir some-target --features some-features
[INFO]: 🎯  Checking for the Wasm target...
[INFO]: 🌀  Compiling to Wasm...
    Finished dev [unoptimized + debuginfo] target(s) in 0.24s
[INFO]: ⬇️  Installing wasm-bindgen...
thread 'main' panicked at 'called `Result::unwrap()` on an `Err` value: 3', src/bindgen.rs:36:14
stack backtrace:
   0: rust_begin_unwind
             at /rustc/84c898d65adf2f39a5a98507f1fe0ce10a2b8dbc/library/std/src/panicking.rs:579:5
   1: core::panicking::panic_fmt
             at /rustc/84c898d65adf2f39a5a98507f1fe0ce10a2b8dbc/library/core/src/panicking.rs:64:14
   2: core::result::unwrap_failed
             at /rustc/84c898d65adf2f39a5a98507f1fe0ce10a2b8dbc/library/core/src/result.rs:1750:5
   3: wasm_pack::bindgen::wasm_bindgen_build
   4: wasm_pack::command::build::Build::step_run_wasm_bindgen
   5: wasm_pack::command::build::Build::run
   6: wasm_pack::command::run_wasm_pack
   7: wasm_pack::main
note: Some details are omitted, run with `RUST_BACKTRACE=full` for a verbose backtrace.

🤔 Expected Behavior

not panic 🙂

👟 Steps to reproduce

See above

🌍 Your environment

Include the relevant details of your environment.
wasm-pack version: 0.11.0 - 48177dc
rustc version: 1.69.0