Lowercase internal constant.

yamlh.go

diff --git a/yamlh.go b/yamlh.go
index 7733b86..1fea365 100644
--- a/yamlh.go
+++ b/yamlh.go
@@ -97,7 +97,7 @@
 // Mapping styles.
 const (
 	// Let the emitter choose the style.
-	YAML_ANY_MAPPING_STYLE yaml_mapping_style_t = iota
+	yaml_ANY_MAPPING_STYLE yaml_mapping_style_t = iota
 
 	yaml_BLOCK_MAPPING_STYLE // The block mapping style.
 	yaml_FLOW_MAPPING_STYLE  // The flow mapping style.