Migrate to Pure ESM

[cassels]

Removing the support for NodeJS v10 and only supporting NodeJS v12 enables native ESM support.

2 of 3 dependencies for dotpref have migrated to pure ESM modules meaning dotpref cannot import them in its current form. Furthermore, semantic-release v19 includes ESM dependencies that yarn trips over resulting in pinning semantic-release to v18.

• chore(deps): update dependency mem to v9 - autoclosed #219
  mem@9.x has dropped support for NodeJS v10 as it is pure ESM.
• chore(deps): update dependency pkg-up to v4 - autoclosed #230
  pkg-up@4.x has dropped support for NodeJS v10 as it is pure ESM.

Currently, Jest support for ESM is experimental but even then, I couldn't get jest@27, ts-jest@27, and TS@4.5 to play nicely together using an ESM build. I'll revisit after jest@28 is released and try again.

Update June 22: jest@28 still only has experimental support for ESM, and I still can't get it working.