fix build headers method jsdoc

Author: lutangar

js/jsonld.js

@@ -1651,10 +1651,10 @@ jsonld.cache = {
 jsonld.acceptHeader = 'application/ld+json, application/json';
 
 /**
- * Build an headers object from custom headers and assert Accept header is not override.
+ * Build an headers object from custom headers and assert `accept` header isn't overridden.
  *
- * @param headers an o
- * @return {*|{}}
+ * @param {Object} headers an object of headers with key as header name and value as header value.
+ * @return {Object} an object of headers with a valid `accept` header.
  */
 jsonld.buildHeaders = function (headers) {
   headers = headers || {};