fix invalid aCollectionOf property definition

ga4gh-beacon#114

framework/json/configuration/entryTypeDefinition.json

@@ -9,9 +9,9 @@
         },
         "aCollectionOf": {
             "description": "If the entry type is a collection of other entry types, (e.g. a Dataset is a collection of Records), then this attribute must list the entry types that could be included. One collection type could be defined as included more than one entry type (e.g. a Dataset could include Individuals or Genomic Variants), in such cases the entries are alternative, meaning that a given instance of this entry type could be of only one of the types (e.g. a given Dataset contains Individuals, while another Dataset could contain Genomic Variants, but not both at once).",
-            "includedConcepts": {
-                "$ref": "../common/basicElement.json",
-                "type": "array"
+            "type": "array",
+            "items": {
+                "$ref": "../common/basicElement.json"
             }
         },
         "additionallySupportedSchemas": {
@@ -65,4 +65,4 @@
     ],
     "title": "",
     "type": "object"
-}
+}