feat: enable source map in build error traces

Author: yyx990803

lib/webpack/createServerConfig.js

@@ -12,6 +12,7 @@ module.exports = function createServerConfig (options, cliOptions) {
   config
     .target('node')
     .externals([/^vue|vue-router$/])
+    .devtool('source-map')
 
   // no need to minimize server build
   config.optimization.minimize(false)