update API reference links

lib/DataCite/API.pm

@@ -5,12 +5,12 @@
 
 =head1 DESCRIPTION
 
-Interact with DataCite API ([1], [2])
+Interact with DataCite MDS API ([1], [2])
 
 =head1 REFERENCES
 
-* [1] https://mds.datacite.org/static/apidoc (dead link as of 2021-09-01)
-* [2] https://mds.test.datacite.org/static/apidoc (dead link as of 2021-09-01)
+* [1] https://support.datacite.org/docs/mds-api-guide
+* [2] https://support.datacite.org/reference/overview
 * [3] http://schema.test.datacite.org/
 * [4] https://blog.datacite.org/cool-dois/
 * [5] http://www.crockford.com/wrmg/base32.html