Description:
------------
NOTE: This bug can replicated only today. 31 Oct 2017.

When adding +1 month using DateTime, it returns incorrect DateTime.

Code: 
$begin = new DateTime("now");
$end = clone $begin;
$end->modify("+1 month");
var_dump($begin,$end);

Outputs dates, where end date is wrong:

object(DateTime)#1 (3) {
  ["date"]=>
  string(26) "2017-10-31 02:41:11.000000"
  ["timezone_type"]=>
  int(3)
  ["timezone"]=>
  string(10) "US/Pacific"
}
object(DateTime)#2 (3) {
  ["date"]=>
  string(26) "2017-12-01 02:41:11.000000"
  ["timezone_type"]=>
  int(3)
  ["timezone"]=>
  string(10) "US/Pacific"
}


Test script:
---------------
$begin = new DateTime("now");
$end = clone $begin;
$end->modify("+1 month");
var_dump($begin,$end);



Expected result:
----------------
object(DateTime)#1 (3) {
  ["date"]=>
  string(26) "2017-10-31 02:41:11.000000"
  ["timezone_type"]=>
  int(3)
  ["timezone"]=>
  string(10) "US/Pacific"
}
object(DateTime)#2 (3) {
  ["date"]=>
  string(26) "2017-11-30 02:41:11.000000"
  ["timezone_type"]=>
  int(3)
  ["timezone"]=>
  string(10) "US/Pacific"
}


Actual result:
--------------
object(DateTime)#1 (3) {
  ["date"]=>
  string(26) "2017-10-31 02:41:11.000000"
  ["timezone_type"]=>
  int(3)
  ["timezone"]=>
  string(10) "US/Pacific"
}
object(DateTime)#2 (3) {
  ["date"]=>
  string(26) "2017-12-01 02:41:11.000000"
  ["timezone_type"]=>
  int(3)
  ["timezone"]=>
  string(10) "US/Pacific"
}