Cannot build the contracts on macOS

Trying to build the contracts directory:

```
» nvm use 14
Now using node v14.16.1 (npm v6.14.12)

» npm install
...
» npm run build
```

the last command returns this:
```bash
» npm run build

> iott-example-contracts@0.1.0 build /Users/simone/Source/github/iotexproject/iott-dapp-example/contracts
> hardhat compile && find artifacts/contracts/**/*.json | grep -v 'dbg' | xargs -i cp {} abis/

Nothing to compile
xargs: illegal option -- i
usage: xargs [-0opt] [-E eofstr] [-I replstr [-R replacements] [-S replsize]]
[-J replstr] [-L number] [-n number [-x]] [-P maxprocs]
[-s size] [utility [argument ...]]
npm ERR! code ELIFECYCLE
npm ERR! errno 1
npm ERR! iott-example-contracts@0.1.0 build: `hardhat compile && find artifacts/contracts/**/*.json | grep -v 'dbg' | xargs -i cp {} abis/`
npm ERR! Exit status 1
npm ERR!
npm ERR! Failed at the iott-example-contracts@0.1.0 build script.
npm ERR! This is probably not a problem with npm. There is likely additional logging output above.

npm ERR! A complete log of this run can be found in:
npm ERR! /Users/simone/.npm/_logs/2021-08-02T15_33_04_117Z-debug.log
```

Full log attached below:
[debug.log](https://github.com/iotexproject/iott-dapp-example/files/6918017/debug.log)