Fix enum definition according to spec.

Relequestual · web-flow · commit 003d88571a3f · 2019-05-21T17:25:19.000+01:00
Issue: #717 enum no longer requires minimum number of items or unique items, in accordance with the spec.
diff --git a/meta/validation.json b/meta/validation.json
@@ -55,9 +55,7 @@
         "const": true,
         "enum": {
             "type": "array",
-            "items": true,
-            "minItems": 1,
-            "uniqueItems": true
+            "items": true
         },
         "type": {
             "anyOf": [
