Fix postinstall #9

[klapperkopp]

This pull request fixes the changes made with #9 , as the change that was done with version v9.6.30

The error that would appear on non-darwin machines would be the following:

coder@cs-57fe3519-fa00-4cfb-8300-824f0bb9e294-7b7f6c6955-p29qx:~/project$ npm i
npm ERR! code 127
npm ERR! path /home/coder/project/node_modules/barcode4nodejs
npm ERR! command failed
npm ERR! command sh -c install_name_tool -change @rpath/libDynamsoftBarcodeReader.dylib @loader_path/libDynamsoftBarcodeReader.dylib build/Release/dbr.node
npm ERR! sh: 1: install_name_tool: not found

npm ERR! A complete log of this run can be found in: /home/coder/.npm/_logs/2024-01-04T13_31_35_440Z-debug-0.log

[klapperkopp]

fixes changes done with #9

[yushulx]

@klapperkopp thanks for your patch 👍