Fix nested array data on Monitor.put

Make sure the `data` param is only reassigned into an array if the
initial `data` param is not an array.

> In the method `Monitor.put`, the assertion `typeof data == 'object'` returns
> `true` whether `data` is an Array or not. This causes `data` to be reassigned
> as a nested array when `Monitor.put` is called with an array as the
> `data` parameter, resulting in an HTTP 500 Error from the API.

lib/monitor.js

@@ -13,7 +13,9 @@ class Monitor {
 
     static async put(data, rollback = false) {
         if (typeof data == 'object') {
-            data = [data];
+            if (!Array.isArray(data)) {
+                data = [data];
+            }
         } else {
             throw new Errors.MonitorNotCreated('Invalid monitor data.');
         }
@@ -125,4 +127,4 @@ class Monitor {
 }
 
 module.exports = Monitor;
-module.exports.default = Monitor;
+module.exports.default = Monitor;