Update rustfmt (#722)

README.md

build.rs

rustfmt.toml

src/lib/ascii_helpers.rs

src/lib/builtins/command_info.rs

src/lib/builtins/conditionals.rs

src/lib/builtins/exec.rs

src/lib/builtins/exists.rs

src/lib/builtins/functions.rs

src/lib/builtins/ion.rs

src/lib/builtins/job_control.rs

src/lib/builtins/man_pages.rs

src/lib/builtins/mod.rs

src/lib/builtins/set.rs

src/lib/builtins/source.rs

src/lib/builtins/test.rs

src/lib/builtins/variables.rs

src/lib/lib.rs

src/lib/parser/arguments.rs

src/lib/parser/assignments/actions.rs