Errors trying to install local development server

I am following this (pretty basic) guide for installing the SquareSpace dev server and am running into permissions errors? 🤷‍♂️

Running macOS Sierra 10.12.6
NPM version is at 6.14.4

Any ideas?

Error: EACCES: permission denied, open 'build/distributions/local-developer/bin/run.bat'
    at Object.openSync (fs.js:439:3)
    at Object.writeFileSync (fs.js:1190:35)
    at main (/usr/local/lib/node_modules/@squarespace/server/scripts/copyfile.js:48:6)
    at Object.<anonymous> (/usr/local/lib/node_modules/@squarespace/server/scripts/copyfile.js:56:1)
    at Module._compile (internal/modules/cjs/loader.js:689:30)
    at Object.Module._extensions..js (internal/modules/cjs/loader.js:700:10)
    at Module.load (internal/modules/cjs/loader.js:599:32)
    at tryModuleLoad (internal/modules/cjs/loader.js:538:12)
    at Function.Module._load (internal/modules/cjs/loader.js:530:3)
    at Function.Module.runMain (internal/modules/cjs/loader.js:742:12)
npm ERR! code ELIFECYCLE
npm ERR! errno 1
npm ERR! @squarespace/server@1.6.2 copyrunscript: `node scripts/copyfile.js build/distributions/local-developer/bin/run.bat darwin:build/distributions/local-developer/bin/osx-local-developer win32:build/distributions/local-developer/bin/win-local-developer.bat linux:build/distributions/local-developer/bin/linux-local-developer build/distributions/local-developer/bin/local-developer`
npm ERR! Exit status 1
npm ERR!
npm ERR! Failed at the @squarespace/server@1.6.2 copyrunscript script.
npm ERR! This is probably not a problem with npm. There is likely additional logging output above.
Command failed: npm run copyrunscript
npm ERR! code ELIFECYCLE
npm ERR! errno 1
npm ERR! @squarespace/server@1.6.2 preinstall: `npm run accept && node scripts/execif.js --exists=build npm run copyrunscript`
npm ERR! Exit status 1
npm ERR!
npm ERR! Failed at the @squarespace/server@1.6.2 preinstall script.
npm ERR! This is probably not a problem with npm. There is likely additional logging output above.

Following this fixed it for me. Except instead I replaced /usr/lib/node_modules/ with /usr/local/lib/node_modules/ since I'm on a Mac.