shellcheck: updateRustDependencies.sh issues

Shellcheck (​​​​​​https://github.com/koalaman/shellcheck) finds the following issues:

In updateRustDependencies.sh line 23:
HERE=`dirname $(realpath $0)`
     ^-- SC2006: Use $(..) instead of legacy `..`.
              ^-- SC2046: Quote this to prevent word splitting.
                         ^-- SC2086: Double quote to prevent globbing and word splitting.


In updateRustDependencies.sh line 24:
TOPLEVEL=`dirname $(dirname $HERE)`
         ^-- SC2006: Use $(..) instead of legacy `..`.
                  ^-- SC2046: Quote this to prevent word splitting.
                            ^-- SC2086: Double quote to prevent globbing and word splitting.


In updateRustDependencies.sh line 27:
CARGO=`which cargo`
      ^-- SC2006: Use $(..) instead of legacy `..`.
       ^-- SC2230: which is non-standard. Use builtin 'command -v' instead.


In updateRustDependencies.sh line 30:
    printf "Error: Couldn't find workspace Cargo.toml in expected location: %s\n" "$TOML"
                                                                              ^-- SC1117: Backslash is literal in "\n". Prefer explicit escaping: "\\n".


In updateRustDependencies.sh line 34:
    printf "Error: Couldn't find directory for Rust dependencies! Expected location: %s\n" "$VENDORED"
                                                                                       ^-- SC1117: Backslash is literal in "\n". Prefer explicit escaping: "\\n".


In updateRustDependencies.sh line 38:
    printf "Error: cargo must be installed and in your \$PATH\n"
                                                             ^-- SC1117: Backslash is literal in "\n". Prefer explicit escaping: "\\n".


In updateRustDependencies.sh line 41:
if test -z `cargo --list | grep vendor` ; then
           ^-- SC2046: Quote this to prevent word splitting.
           ^-- SC2006: Use $(..) instead of legacy `..`.


In updateRustDependencies.sh line 42:
    printf "Error: cargo-vendor not installed\n"
                                             ^-- SC1117: Backslash is literal in "\n". Prefer explicit escaping: "\\n".


In updateRustDependencies.sh line 45:
$CARGO vendor -v --locked --explicit-version --no-delete --sync $TOML $VENDORED
                                                                ^-- SC2086: Double quote to prevent globbing and word splitting.
                                                                      ^-- SC2086: Double quote to prevent globbing and word splitting.