Fix ENOENT when running from working directory without package.json (#516)

Author: s0ph1e

lib/config/defaults.js

@@ -1,6 +1,4 @@
-import fs from 'fs';
-const packageJson = JSON.parse(fs.readFileSync('./package.json', 'utf8'));
-const defaultRequestUserAgent = `${packageJson.name}/${packageJson.version} (https://github.com/website-scraper/node-website-scraper)`;
+const defaultRequestUserAgent = 'website-scraper (https://github.com/website-scraper/node-website-scraper)';
 
 const config = {
 	defaultFilename: 'index.html',