Updated install command for Homebrew

[chinleung]

The command in the README.md would throw the following error:

Error: `brew cask` is no longer a `brew` command. Use `brew <command> --cask` instead.

I've updated it for the correct command.

[CLAassistant]

Thank you for your submission! We really appreciate it. Like many open source projects, we ask that you all sign our Contributor License Agreement before we can accept your contribution.
1 out of 2 committers have signed the CLA.

✅ chinleung
❌ Mike Renoir

---

Mike Renoir seems not to be a GitHub user. You need a GitHub account to be able to sign the CLA. If you have already a GitHub account, please add the email address used for this commit to your account.
_{You have signed the CLA already but the status is still pending? Let us recheck it.}

[clyde870]

Suggested change

```

[jbgy]

oh wait you already pull requested it xdd

[chinleung]

oh wait you already pull requested it xdd

What do you mean? 👀

[jbgy]

oh wait you already pull requested it xdd

What do you mean? 👀

I was trying to fix it too