docs: fix the CHANGELOG to reflect 3.x breaking changes

[JustinBeckwith]

Fixes #613. There were errors in the changelog in the 3.0 release. I already cleaned up the release notes in the GitHub release.

[codecov]

Codecov Report

Merging #671 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #671   +/-   ##
=======================================
  Coverage   88.29%   88.29%           
=======================================
  Files          18       18           
  Lines         769      769           
  Branches       83       83           
=======================================
  Hits          679      679           
  Misses         79       79           
  Partials       11       11

---

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[codecov]

Codecov Report

Merging #671 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #671   +/-   ##
=======================================
  Coverage   88.29%   88.29%           
=======================================
  Files          18       18           
  Lines         769      769           
  Branches       83       83           
=======================================
  Hits          679      679           
  Misses         79       79           
  Partials       11       11

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update dffd1cc...782813e. Read the comment docs.

[bcoe]

👍 let's make this not manual as soon as humanly possible 😄