Error: Cannot find module 'es6-weak-map'

[tgandrews]

Recreation steps

1. Create a new node project
2. Run npm install --save deep-map
3. Create an index.js with

const deepMap = require("deep-map");
console.log("hello world");

4. Run the index.js

Expect

hello world

Actual

internal/modules/cjs/loader.js:583
    throw err;
    ^

Error: Cannot find module 'es6-weak-map'
    at Function.Module._resolveFilename (internal/modules/cjs/loader.js:581:15)
    at Function.Module._load (internal/modules/cjs/loader.js:507:25)
    at Module.require (internal/modules/cjs/loader.js:637:17)
	...

Reason

es6-weak-map was moved to being a dev dependency in 1a98c4e
but it should not have been