[FIX] flatten ARRAY Object @kbn.flatten_json()

This change will flatten the array of objects.

Example : 

var objs = [{Name:"name1"},{Name:"name2"},{Name:"name3"}] 
console.log(kbn.flatten_json(objs)) will return flatten objects
objs.0.Name : name1
objs.1.Name : name2
objs.2.Name : name3

and not {Name:"name1"},{Name:"name2"},{Name:"name3"} as it was in the previous version