Added temporary fix for london hardfork compatibility

[kautukkundan]

What does this pull request do? Explain your changes. (required)

The current solidity-coverage version overrides the gasPrice during execution and sets it equal to 1. This creates an issue with the EIP-1559 "baseFeePerGas". There is an open issue sc-forks/solidity-coverage/issues/652 to deal with this. This PR includes a temporary and "hacky" solution to overcome the issue by setting the initialBaseFeePerGas equal to 0 in the hardhat network config. However, moving forward this should not be the final solution.

Specific updates (required)

• update hardhat version to v2.6.0
• set initialBaseFeePerGas equal to 0 in the hardhat config

How did you test each of these updates (required)

ran yarn test:coverage

Does this pull request close any open issues?

closes #447

Checklist:

• [x] README and other documentation updated
• [x] All tests using yarn run test pass
• [x] need to merge #456 before merging this

[coveralls]

Pull Request Test Coverage Report for Build 1140562675

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 98.167%

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Totals
Change from base Build 1137227852:	0.0%
Covered Lines:	851
Relevant Lines:	865

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💛 - Coveralls

[kyriediculous]

RE the dependency issue this looks good to me, I think I installed it the wrong way (outdated documentation from a blog rather than the official one) which then persisted itself in the lock file. Not sure why it wasn't caught earlier either, maybe with the move to yarn.

Test update also looks good to me, let's change the base to nv/next maybe since that has the conflicts resolved with streamflow and then we can merge nv/next into next and then next into streamflow. WDYT ?