This task allows a user to update the L2 gas price using hardhat.
An example of doing so would be:

```bash
$ export CONTRACTS_DEPLOYER_KEY=0x..
$ CONTRACTS_RPC_URL=https://kovan.optimism.io npx hardhat set-l2-gasprice \
    --l2-gas-price 1
```

This hardcodes the predeploy address of the `OVM_GasPriceOracle` smart
contract and the Owner must be used to do the updating, otherwise the
transaction will revert.