Update JSON and Date types

Author: Caitlin Bales (MSFT)

src/GraphODataTemplateWriter/CodeHelpers/PHP/TypeHelperPHP.cs

@@ -41,6 +41,7 @@ public static string GetTypeString(this OdcmType @type)
             switch (@type.Name)
             {
                 case "String":
+                case "Json":
                     return "string";
                 case "Int8":
                 case "Int16":
@@ -52,6 +53,7 @@ public static string GetTypeString(this OdcmType @type)
                 case "Guid":
                     return "UUID";
                 case "DateTimeOffset":
+                case "Date":
                     return "datetime";
                 case "Boolean":
                     return "bool";