make logger optional so code can be re-used for CLI interface

lib/services/crawler.js

@@ -1,11 +1,14 @@
 const request = require('request')
 
 const crawl = async (url, { logger }) => {
-  logger.log({
-    message: `Crawl started for url: ${url}`,
-    level: 'info',
-    service: 'parser',
-  })
+  if (logger) {
+    logger.log({
+      message: `Crawl started for url: ${url}`,
+      level: 'info',
+      service: 'parser',
+    })
+  }
+
   return new Promise((resolve, reject) => {
     request({
       url,