app.js bundle is not minified

[claisne]

When building, the app bundle is not minified:

Steps to reproduce:
gatsby new test
gatsby build

Begining of the bundle:

webpackJsonp([15178676390636814000],{

/***/ "./.cache/api-runner-browser.js":
/***/ (function(module, exports) {

	"use strict";
	
	exports.__esModule = true;
	exports.apiRunner = apiRunner;
	exports.apiRunnerAsync = apiRunnerAsync;
	var plugins = [];
	// During bootstrap, we write requires at top of this file which looks
	// basically like:
	// var plugins = [
	//   require('/path/to/plugin1/gatsby-browser.js'),
	//   require('/path/to/plugin2/gatsby-browser.js'),
	// ]
	

Node version: 8.4.0
Yarn version: 0.24.6
Gatsby version: 1.8.13