Update CodegenProperty.java

Added a "items" field to keep track of the inner type to be accessed in the mustache templates

modules/swagger-codegen/src/main/java/io/swagger/codegen/CodegenProperty.java

@@ -34,4 +34,6 @@ public class CodegenProperty {
     public boolean isEnum;
     public List<String> _enum;
     public Map<String, Object> allowableValues;
+    public CodegenProperty items;
+
 }