update instances of collectibles to nfts

[NidhiKJha]

This PR is to update collectibles to nfts.

Reference: MetaMask/metamask-extension#16889

Code for Abis and bytecode:

pragma solidity ^0.8.7;

import "@openzeppelin/contracts@4.8.1/token/ERC721/ERC721.sol";

contract MyToken is ERC721 {
    constructor() ERC721("NFT Token", "NFT") {}

    function safeMint(uint256 tokenId) public {
        _safeMint(msg.sender, tokenId);
    }
}

[Gudahtt]

In a recent PR, the source code for the old "Collectibles" contract was added to the repository (in the contracts directory). Could you replace that contract with the source code for the new one?

[Gudahtt]

Hmm, I tried compiling this in Remix but got an error about Strings already being declared. I don't quite understand why, but, it went away with I removed the @4.8.1 or added it to the other two imports. Perhaps they should all be using the same version of @openzeppelin/contracts.