Update Symfony YAML library to support whole number floats

See #2310093: Config install and import should map from storage record not set properties directly

Include the better upstream fix - https://github.com/symfony/symfony/pull/11976

The issue we have to best illustrated by the following code:

$yaml = new \Symfony\Component\Yaml\Yaml();

$expected = array('float' => (float) 1);
$test = $yaml->parse($yaml->dump($expected));

if ($expected === $test) {
  print "match!\n";
}
else {
  var_dump($test);
}

which outputs

array(1) {
  'float' =>
  int(1)
}

Our float has become an integer!