Fix #198 (#781)

* Add new function to Render interface for writing content type only

* Add support for the new function in Render interface for writing content-type only

* Fix unhandled merge conflict in context_test.go

* Update vendor.json

render/yaml.go

@@ -17,7 +17,7 @@ type YAML struct {
 var yamlContentType = []string{"application/x-yaml; charset=utf-8"}
 
 func (r YAML) Render(w http.ResponseWriter) error {
-	writeContentType(w, yamlContentType)
+	r.WriteContentType(w)
 
 	bytes, err := yaml.Marshal(r.Data)
 	if err != nil {
@@ -27,3 +27,7 @@ func (r YAML) Render(w http.ResponseWriter) error {
 	w.Write(bytes)
 	return nil
 }
+
+func (r YAML) WriteContentType(w http.ResponseWriter) {
+	writeContentType(w, yamlContentType)
+}