fixes #91 update one test case to ensure compatibility of Java 6

Author: stevehu

src/test/java/com/networknt/schema/CustomMetaSchemaTest.java

@@ -80,7 +80,7 @@ private List<String> readStringList(JsonNode node) {
             if (!node.isArray()) {
                 throw new JsonSchemaException("Keyword enum needs to receive an array");
             }
-            ArrayList<String> result = new ArrayList<>(node.size());
+            ArrayList<String> result = new ArrayList<String>(node.size());
             for (JsonNode child : node) {
                 result.add(child.asText());
             }