Update API example; (DOECODE-946)

Author: Tim Sowers

src/main/java/gov/osti/services/Metadata.md

@@ -574,7 +574,7 @@ metadata fields.
 "documentation_url": "",
 "country_of_origin": "United States",
 "keywords": "doecode",
-"license":["Apache License 2.0"],
+"licenses":["Apache License 2.0"],
 "release_date":"2017-08-23",
 "links": [
     {"rel": "citation",