Merge pull request #5261 from Countly/drill-params-fix

[drill][fix] allow "prevMonth" as period param

Author: Cookiezaurs

api/lib/countly.common.js

@@ -786,10 +786,16 @@ countlyCommon.isValidPeriodParam = function(period) {
     }
 
     if (typeof period === 'object') {
-        return Object.prototype.hasOwnProperty.call(period, 'since') || Object.prototype.hasOwnProperty.call(period, 'period');
+        if (Object.prototype.hasOwnProperty.call(period, 'period')) {
+            return countlyCommon.isValidPeriodParam(period.period);
+        }
+        else {
+            return Object.prototype.hasOwnProperty.call(period, 'since');
+        }
     }
 
     return period === 'month' ||
+        period === 'prevMonth' ||
         period === 'day' ||
         period === 'yesterday' ||
         period === 'hour' ||