Use the CLoader when present to validate yaml

pre_commit_hooks/check_yaml.py

diff --git a/pre_commit_hooks/check_yaml.py b/pre_commit_hooks/check_yaml.py
index 0085807..293352f 100644
--- a/pre_commit_hooks/check_yaml.py
+++ b/pre_commit_hooks/check_yaml.py
@@ -6,6 +6,12 @@
 import yaml
 
 
+try:
+    from yaml.cyaml import CLoader as Loader
+except ImportError:  # pragma: no cover (no libyaml-dev / pypy)
+    Loader = yaml.Loader
+
+
 def check_yaml(argv=None):
     parser = argparse.ArgumentParser()
     parser.add_argument('filenames', nargs='*', help='Yaml filenames to check.')
@@ -14,7 +20,7 @@
     retval = 0
     for filename in args.filenames:
         try:
-            yaml.load(open(filename))
+            yaml.load(open(filename), Loader=Loader)
         except yaml.YAMLError as exc:
             print(exc)
             retval = 1