Verify that depth is set when you crawl #2806 (#2807)

lib/plugins/crawler/index.js

@@ -4,6 +4,7 @@ const path = require('path');
 const merge = require('lodash.merge');
 const log = require('intel').getLogger('sitespeedio.plugin.crawler');
 const Crawler = require('simplecrawler');
+const throwIfMissing = require('../../support/util').throwIfMissing;
 
 const defaultOptions = {
   depth: 3
@@ -11,6 +12,7 @@ const defaultOptions = {
 
 module.exports = {
   open(context, options) {
+    throwIfMissing(options.crawler, ['depth'], 'crawler');
     this.options = merge({}, defaultOptions, options.crawler);
     this.make = context.messageMaker('crawler').make;
     this.basicAuth = options.browsertime