pre-commit hook: fix shellcheck SCSC2181

Check exit code directly with e.g. if mycmd;
not indirectly with $?

https://github.com/koalaman/shellcheck/wiki/SC2181

shell/hooks/pre-commit.sh

@@ -20,8 +20,7 @@ if [[ -n "${nix_files[@]}" ]]; then
 fi
 
 # check editorconfig
-editorconfig-checker -- "${all_files[@]}"
+if ! editorconfig-checker -- "${all_files[@]}"; then
-if [[ $? != '0' ]]; then
   printf "%b\n" \
     "\nCode is not aligned with .editorconfig" \
     "Review the output and commit your fixes" >&2