feat: drop support for webpack 4

BREAKING CHANGE: Only webpack 5 is supported.

.github/workflows/build.yml

@@ -17,10 +17,6 @@ jobs:
     strategy:
       matrix:
         node-version: [12.x, 14.x, 16.x, 18.x]
-        webpack-version: [default, ^4.0.0]
-        exclude:
-          - node-version: 18.x
-            webpack-version: ^4.0.0
 
     steps:
       - name: Checkout
@@ -42,10 +38,6 @@ jobs:
         if: ${{ steps.cache-nodemodules.outputs.cache-hit != 'true' }}
         run: yarn install --frozen-lockfile --non-interactive
 
-      - name: Install webpack
-        if: ${{ matrix.webpack-version != 'default' }}
-        run: yarn add --dev webpack@${{ matrix.webpack-version }}
-
       - name: Unit tests
         run: yarn test --ci
 

README.md

@@ -14,7 +14,8 @@
 
 <h2 align="center">Requirements</h2>
 
-- Version 5 of `grunt-webpack` supports webpack version 4 and 5 and (optional) `webpack-dev-server` version 4.
+- Version 6 of `grunt-webpack` supports webpack 5 and (optional) `webpack-dev-server` version 4.
+- For webpack 4 use version 5 of `grunt-webpack`
 
 <h2 align="center">Install</h2>
 

package.json

@@ -22,7 +22,7 @@
     "tasks"
   ],
   "peerDependencies": {
-    "webpack": "^4.0.0 || ^5.0.0"
+    "webpack": "^5.0.0"
   },
   "license": "MIT",
   "keywords": [

src/plugins/CachePluginFactory.js

@@ -1,14 +1,6 @@
 "use strict";
 
-let CachePlugin;
-try {
-  // webpack 5
-  CachePlugin = require("webpack/lib/cache/MemoryCachePlugin");
-} catch (e) {
-  // webpack 4
-  // eslint-disable-next-line import/no-unresolved,import/extensions
-  CachePlugin = require("webpack/lib/CachePlugin");
-}
+const CachePlugin = require("webpack/lib/cache/MemoryCachePlugin");
 
 class CachePluginFactory {
   constructor() {