Bump web3 from 5.11.0 to 5.12.0 in /requirements

[dependabot]

Bumps web3 from 5.11.0 to 5.12.0.

Changelog

Sourced from web3's changelog.

v5.12.0 (2020-07-16)

Features

- Update `web3.pm` and `ethpm` module to EthPM v3 specification. (`[#1652](https://github.com/ethereum/web3.py/issues/1652) <https://github.com/ethereum/web3.py/issues/1652>`__)
- Allow consumer to initialize `HttpProvider` with their own `requests.Session`.  This allows the `HttpAdapter` connection pool to be tuned as desired. (`[#1469](https://github.com/ethereum/web3.py/issues/1469) <https://github.com/ethereum/web3.py/issues/1469>`__)
Improved Documentation

• Use ethpm v3 packages in examples documentation. ([#1683](https://github.com/ethereum/web3.py/issues/1683) <https://github.com/ethereum/web3.py/issues/1683>__)
• Modernize the deploy contract example. ([#1679](https://github.com/ethereum/web3.py/issues/1679) <https://github.com/ethereum/web3.py/issues/1679>__)
• Add contribution guidelines and a code of conduct. ([#1691](https://github.com/ethereum/web3.py/issues/1691) <https://github.com/ethereum/web3.py/issues/1691>__)

Misc

- `[#1687](https://github.com/ethereum/web3.py/issues/1687) <https://github.com/ethereum/web3.py/issues/1687>`__
- `[#1690](https://github.com/ethereum/web3.py/issues/1690) <https://github.com/ethereum/web3.py/issues/1690>`__
v5.12.0-beta.3 (2020-07-15)
Bugfixes

• Include ethpm-spec solidity examples in distribution. ([#1686](https://github.com/ethereum/web3.py/issues/1686) <https://github.com/ethereum/web3.py/issues/1686>__)

v5.12.0-beta.2 (2020-07-14)

Bugfixes

- Support ethpm-spec submodule in distributions. (`[#1682](https://github.com/ethereum/web3.py/issues/1682) <https://github.com/ethereum/web3.py/issues/1682>`__)
Improved Documentation

• Modernize the deploy contract example. ([#1679](https://github.com/ethereum/web3.py/issues/1679) <https://github.com/ethereum/web3.py/issues/1679>__)
• Use ethpm v3 packages in examples documentation. ([#1683](https://github.com/ethereum/web3.py/issues/1683) <https://github.com/ethereum/web3.py/issues/1683>__)

Commits

• b9d7677 Bump version: 5.12.0-beta.3 → 5.12.0
• 5116893 Compile release notes
• 583d583 Introduce contribution and code of conduct docs (#1691)
• a008f9d adopt trinity's newsfragment validation (#1690)
• 21914f6 Compile release notes
• 695f6c3 fix 'make notes' docs
• 3141cd8 add newsfragment
• dc7daa3 update release documentation
• 7565319 unbundle notes from release command
• 4dd9deb Bump version: 5.12.0-beta.2 → 5.12.0-beta.3
• Additional commits viewable in compare view

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[dependabot]

Superseded by #5.