chore: use npm workspaces

Closes istanbuljs#703

README.md

@@ -31,7 +31,7 @@ _You're probably actually looking for one of the following repos:_
 
 Contributing to the packages contained in this repo is easy:
 
-1. after checking out, run `npm install` (this will run the lerna build).
+1. after checking out, run `npm install` (you need **npm>=7**, since this monorepo is using [npm workspaces](https://docs.npmjs.com/cli/v8/using-npm/workspaces)).
 2. to run all tests, simply run `npm test` in the root directory.
 3. to run tests for a single package `cd package/:name` and run
    `npm test` within the package's folder.

package.json

@@ -6,9 +6,9 @@
   "scripts": {
     "test": "cross-env NODE_ENV=test nyc mocha --timeout 30000 packages/*/test{,/*}.js",
     "posttest": "eslint .",
-    "fix": "eslint . --fix",
-    "postinstall": "bash scripts/install.sh"
+    "fix": "eslint . --fix"
   },
+  "workspaces": ["packages/*"],
   "repository": {
     "type": "git",
     "url": "git@github.com:istanbuljs/istanbuljs.git"
@@ -45,8 +45,10 @@
     ]
   },
   "engines": {
-    "node": ">=8"
+    "node": ">=8",
+    "npm": ">=7"
   },
+  "engineStrict": true,
   "prettier": {
     "singleQuote": true,
     "tabWidth": 4