Add New Zealand Dollar to currency options

[ScreamingHawk]

Fixes: -

Explanation:
I was annoyed that I wasn't able to view my wallet balance in my own currency. Had a quick dig through the code and found that it's a simple fix to include it.
Double checked against the API that the currency is listed here: /~https://github.com/MetaMask/controllers/blob/develop/src/apis/crypto-compare.ts

If you are happy to accept this I can push the same change to the mobile repo as well.

Manual testing steps:

• Navigate to Settings
• Select Currency Conversion drop down
• Select New Zealand Dollar from the drop down
• Confirm wallet value is accurate

[github-actions]

CLA Signature Action: All authors have signed the CLA. You may need to manually re-run the blocking PR check if it doesn't pass in a few minutes.

[ScreamingHawk]

I have read the CLA Document and I hereby sign the CLA

[brad-decker]

This LGTM! Thanks for the contribution @ScreamingHawk