title: Expected argument of type "string", "stdClass" given Error
body: <p>I'm using mailchimp-api-v3 for nodejs. I'm currently trying to update a user's tag but sometimes this error pops up and I have no idea what it means. I searched around but it doesn't seem like a lot of devs have encountered it. </p>
  
  <p>Any suggestions are welcomed.</p>
  
  <pre><code>try {
  await mailchimp.post('/lists/' + listIDUsers + '/members/' + crypto.createHash('md5').update(profileSnap.val().email.toLowerCase()).digest("hex") + '/tags', {
          tags: [{name: "traveler", status: "active"}]
      });
  } catch (error) {
  if (error.status === 404) {
  await mailchimp.post('/lists/' + listIDUsers + '/members', {
              email_address: profileSnap.val().email,
              status: 'subscribed',
              merge_fields: {
                  "FNAME": profileSnap.val().firstName,
                  "LNAME": profileSnap.val().lastName,
                  "UID": uid,
                  "EMAIL": profileSnap.val().email
              },
              tags: [{name: "traveler", status: "active"}]
          });
      } else {
          console.log("Issue for: " + uid);
          console.log(error);
   }
  </code></pre>
  
  <p>The error:</p>
  
  <pre><code>Error: Expected argument of type "string", "stdClass" given
      at Request._callback (/srv/node_modules/mailchimp-api-v3/index.js:506:30)
      at Request.self.callback (/srv/node_modules/request/request.js:185:22)
      at emitTwo (events.js:126:13)
      at Request.emit (events.js:214:7)
      at Request.&lt;anonymous&gt; (/srv/node_modules/request/request.js:1161:10)
      at emitOne (events.js:116:13)
      at Request.emit (events.js:211:7)
      at IncomingMessage.&lt;anonymous&gt; (/srv/node_modules/request/request.js:1083:12)
      at Object.onceWrapper (events.js:313:30)
      at emitNone (events.js:111:20)
      at IncomingMessage.emit (events.js:208:7)
      at endReadableNT (_stream_readable.js:1064:12)
      at _combinedTickCallback (internal/process/next_tick.js:139:11)
      at process._tickDomainCallback (internal/process/next_tick.js:219:9)
  </code></pre>