Update ERC-20: Fix broken link on erc-20.md

[shahbaz17]

Fix broken link under Implementation for OpenZeppelin and ConsenSys implementation

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[eip-review-bot]

File ERCS/erc-20.md

Requires 2 more reviewers from @axic, @gcolvin, @lightclient, @SamWilsn

[github-actions]

The commit d21d07a (as a parent of 7883f61) contains errors.
Please inspect the Run Summary for details.

[SamWilsn]

The current links appear to be working: https://eips.ethereum.org/EIPS/eip-20#implementation

[shahbaz17]

These two links are still not working. When opening through the Markdown file. Can you confirm once?

It's here as I see: https://github.com/ethereum/ERCs/blob/master/assets/erc-20/Consensys-EIP20.sol and https://github.com/ethereum/ERCs/blob/master/assets/erc-20/OpenZeppelin-ERC20.sol

[SamWilsn]

None of the asset links work in the GitHub markdown preview, unfortunately.