getCreatedTime returns string instead of integer

Problem/Motivation

The phpdocs of getCreatedTime mention that the timestamp will be returned as integer. While it is currently returning a string.
This leads to bugs when you do strict comparison with the changed time which is correctly returning an integer.

Steps to reproduce

if ($comment->getCreatedTime() !== $comment->getChangedTime()) {
  // Statement is always true
}

Proposed resolution

Convert the value to int, just like all other timestamp methods.