Update gas price fields for 1559

[adamgoth]

Instead of setting gasPrice, we set maxFeePerGas and maxPriorityFeePerGas. maxPriorityFeePerGas is hardcoded to 2.5 gwei.

More info for the gas fields expected in web3 sendTransaction: https://web3js.readthedocs.io/en/v1.5.2/web3-eth.html#sendtransaction

More info for changes from infura: https://blog.infura.io/london-fork/

[codecov]

Codecov Report

Merging #315 (1e184b5) into dev (018cbbb) will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##              dev     #315   +/-   ##
=======================================
  Coverage   86.15%   86.16%           
=======================================
  Files         139      139           
  Lines        6351     6352    +1     
  Branches     1263     1263           
=======================================
+ Hits         5472     5473    +1     
  Misses        873      873           
  Partials        6        6           

Impacted Files	Coverage Δ
packages/dai/src/eth/TransactionManager.js	91.25% <100.00%> (+0.05%)	⬆️

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