remove condition due to 'this.options.dev' is always false

Signed-off-by: Clark Du <clark.duxin@gmail.com>

lib/core/renderer.js

@@ -243,7 +243,7 @@ export default class Renderer extends Tapable {
         path: this.publicPath,
         handler: serveStatic(distDir, {
           index: false, // Don't serve index.html template
-          maxAge: (this.options.dev ? 0 : '1y') // 1 year in production
+          maxAge: '1y' // 1 year in production
         })
       })
     }