fix(cli): Don’t use backticks to unbreak zsh compdef

[d125q]

Currently, the generated zsh compdef contains something along the
lines of

(( $+functions[_fontship_commands] )) ||
_fontship_commands() {
    local commands; commands=(
        "make:Build specified target(s) with `make`" \
"setup:Configure a font project repository" \
"status:Show status information about setup, configuration, and build state" \
"help:Prints this message or the help of the given subcommand(s)" \
    )
    _describe -t commands 'fontship commands' commands "$@"
}

I.e., it performs command substitution on ‘make’, which in the best
case fails with something along the lines of “make: *** No targets
specified and no makefile found. Stop.” and in the worst case ends up
running ‘make’ for you.

This issue should probably be brought up to clap-rs/clap so that it is
made to use single quotes instead of double quotes and escape
everything correctly.

For now, this commit fixes the issue by using “smart quotes” instead
of backticks.

[alerque]

Wow good catch. Yes this is something that should be reported is reported upstream in Clap, it shouldn't be generating dangerous executable code!