v2.2.2 Release: Backports MuirGlacier difficulty adjustments

[holgerd77]

[DO NOT MERGE THIS PR!!!]

Backport release analog to https://github.com/ethereumjs/ethereumjs-block/pull/77. This is branched off the release/v2.2.1 branch, to be released as described here.

• [x] TravisCI runs through
• [x] Confirmation that browser tests run locally
• [x] Reviewed and approved
• [x] Publish npm release from local branch
• [x] Create GitHub release with release/v2.2.2 as a target branch
• [x] Do not merge but close this PR, do not delete the branch

Open for review.

[holgerd77]

Ok, a bit annoying to do this old/already outdated work, but I also fixed the Travis xvfb issue analog to https://github.com/ethereumjs/ethereumjs-util/pull/221 to get at least the Node tests passing here.

This is done, now finally ready for review so that we can release (and subsequently do a blockchain and then the VM release on MuirGlacier).

[evertonfraga]

thanks for putting it together. i was planning to do it tonight.

[holgerd77]

No prob, let me know if you can approve.

[evertonfraga]

i assume ill need to approve again after the conflicts get solved. i can help with that if you want.

[holgerd77]

@evertonfraga Ah no, conflict solving is not necessary here since this won't get merged. This is just because the PR is opened against master.

[holgerd77]

Just released as v2.2.2 on npm.

[holgerd77]

@evertonfraga if you want you can already prepare a release on the blockchain library with an update on the block dependency + release notes (including the PRs merged since the last release).

[evertonfraga]

👍🏼