fix stringify

Author: shuding

packages/next/build/entries.ts

@@ -175,6 +175,7 @@ export function createEntrypoints(
       serverWeb[serverBundlePath] = finalizeEntrypoint({
         name: '[name].js',
         value: `next-middleware-ssr-loader?${stringify({
+          dev: false,
           page,
           stringifiedConfig: JSON.stringify(config),
           absolute500Path: pages['/500'] || '',

packages/next/build/webpack/loaders/next-middleware-ssr-loader/index.ts

@@ -65,7 +65,7 @@ export default async function middlewareSSRLoader(this: any) {
 
       // renderOpts
       buildId: ${JSON.stringify(buildId)},
-      dev: ${JSON.stringify(dev)},
+      dev: ${dev},
       env: process.env,
       supportsDynamicHTML: true,
       concurrentFeatures: true,