Run Rustfmt on Shell Module

src/shell/assignments.rs

src/shell/binary.rs

src/shell/completer.rs

src/shell/directory_stack.rs

src/shell/flags.rs

src/shell/flow.rs

src/shell/flow_control.rs

src/shell/history.rs

src/shell/job.rs

src/shell/mod.rs

src/shell/pipe_exec/foreground.rs

src/shell/pipe_exec/job_control.rs

src/shell/pipe_exec/mod.rs

src/shell/signals.rs

src/shell/status.rs