fix identifier bug introduced in previous PR

eossr/metadata/tests/samples/codemeta_contributors_sample.json

@@ -13,7 +13,7 @@
         "name": "Author-and-Creator-same-person-affiliation"
       },
       "email": "Author-and-Creator-same-person-email",
-      "identifier": "Author-and-Creator-same-person-identifier"
+      "@id": "Author-and-Creator-same-person-identifier"
     }
   ],
   "creator": {
@@ -25,7 +25,7 @@
       "name": "Author-and-Creator-same-person-affiliation"
     },
     "email": "Author-and-Creator-same-person-email",
-    "identifier": "Author-and-Creator-same-person-identifier"
+    "@id": "Author-and-Creator-same-person-identifier"
   },
   "maintainer": {
     "@type": "Person",
@@ -35,7 +35,7 @@
       "@type": "Organization",
       "name": "Maintainer-affiliation"
     },
-    "identifier": "https://orcid.org/0000-0000-0000-0000"
+    "@id": "https://orcid.org/0000-0000-0000-0000"
   },
   "contributor": [
     {