trying the npm fix

package.json

@@ -21,11 +21,11 @@
     "lint:js": "eslint --fix --cache lib test",
     "lint:json": "prettier --write codecov.yml .circleci/config.yml .eslintrc",
     "lint:package": "prettier --write package.json --plugin=prettier-plugin-package",
-    "posttest": "npm install webpack@^4.44.2",
+    "posttest": "node set-webpack-version.js \"^4.44.2\" && npm install",
     "security": "npm audit --audit-level=moderate",
     "test": "npm run test:v4 && npm run test:v5",
     "test:v4": "ava",
-    "test:v5": "npm install webpack@^5.0.0 --no-save && ava"
+    "test:v5": "node set-webpack-version.js \"^5\" && npm install && ava"
   },
   "files": [
     "lib",

set-webpack-version.js

@@ -0,0 +1,25 @@
+/*
+ * This file sets Webpack version - both devDependencies and peerDependencies.
+ *
+ * This is, for some reason, needed with Windows and maybe npm 6. Running
+ * "npm install webpack -D" AND manually updating the peerDependencies
+ * (because npm 6 does not do that but npm 7 does) is not enough. For some
+ * reason why must, by hand, update the package.json file first and then
+ * run a normal "npm install".
+ */
+const fs = require('fs');
+const path = require('path');
+
+const version = process.argv[2];
+if (!version) {
+  console.log('Please pass the webpack version - "^4" or "^5" - as an argument.');
+
+  process.exit(1);
+}
+
+const packageData = JSON.parse(fs.readFileSync(path.join(__dirname, 'package.json')));
+packageData.peerDependencies.webpack = version;
+
+packageData.devDependencies.webpack = version;
+
+fs.writeFileSync(path.join(__dirname, 'package.json'), JSON.stringify(packageData, null, 2));