common: set the default hard fork to merge

[g11tech]

set the default hard fork to merge

Closes #2015

[codecov]

Codecov Report

Merging #2087 (4d6dc6d) into master (2f9f3ea) will decrease coverage by 0.01%.
The diff coverage is 50.00%.

Flag	Coverage Δ
block	83.81% <ø> (ø)
blockchain	80.54% <ø> (+0.43%)	⬆️
client	78.29% <ø> (-0.05%)	⬇️
common	95.00% <0.00%> (ø)
devp2p	82.66% <ø> (-0.26%)	⬇️
ethash	90.81% <ø> (ø)
evm	40.97% <ø> (ø)
statemanager	84.55% <ø> (ø)
trie	81.35% <ø> (ø)
tx	92.18% <100.00%> (ø)
util	87.22% <ø> (ø)
vm	78.40% <ø> (ø)

Flags with carried forward coverage won't be shown. Click here to find out more.

[gabrocheleau]

Looks good! However some merged-related tests are now failing in merge.spec.ts:

• 'should mine and stop at the merge (PoA)'
• 'should mine and stop at the merge (PoW)'

Didn't check in detail but perhaps all that's required is to manually provide a pre-merge HF for those test cases

[g11tech]

thanks @acolytec3 for fixes, got distracted after pushing initial PR 😉

[gabrocheleau]

LGTM! 👍🏼

[holgerd77]

Nice, cool, didn't assume this to be so narrowly scoped respectively going through with so few changes. 😀 🤩 Seems Emmett already did a lot of base work here with adding the explicit HF (Common) instantiations in the round before upgrading to London.

Great!