Use Array.isArray() instead of AeroGear.isArray()

Currently we define a method called AeroGear.isArray, to test if an object is an Array.

the native Array.isArray() is available in all browsers that we are supporting, so we should just use that.

The plan should be to deprecate this method and remove it in 2.0. the AeroGear.isArray method will just return the native result

It is only used internally, but a user could be using it externally