fix: rollback to previous check for fs

Author: wood1986

src/BundleAnalyzerPlugin.js

@@ -31,15 +31,15 @@ class BundleAnalyzerPlugin {
   }
 
   apply(compiler) {
-    const isWebpack5 = !!(compiler.webpack);
+    const isFromWebpackDevServer = process.env.WEBPACK_SERVE === 'true';
 
     this.compiler = compiler;
 
     this.logger = require('webpack/lib/logging/runtime')?.getLogger(PLUGIN_NAME)
       || new Logger(this.opts.logLevel);
 
     const done = (stats, callback) => {
-      this.fs = isWebpack5 ? compiler.outputFileSystem : require('fs');
+      this.fs = isFromWebpackDevServer ? compiler.outputFileSystem : require('fs');
       callback = callback || (() => {});
 
       const actions = [];