Update Spyc to latest version

https://github.com/mustangostang/spyc/commit/4e2a585

Ran scripts/yaml-tests.php with the following results:

array(2) {
  ["syck"]=>
  float(21.254214048386)
  ["spyc"]=>
  float(0.45939993858337)
}
array(2) {
  ["syck"]=>
  int(1125147)
  ["spyc"]=>
  int(1290993)
}
array(2) {
  ["syck"]=>
  int(1126734)
  ["spyc"]=>
  int(1290993)
}

This means syck is about 40x slower when using hhvm with no significant
difference in memory usage. Also the output files are identical except
a couple of things which I will fix in a separate commit.

Change-Id: Ibec61251c45e0eef1210c99761838aea8ca98421