Postgres 9.6 compatibility

[MhdSyrwan]

Fixes #2
Related to #1

[hynra]

@0x777 Can you review this?

[hynra]

Still got an error on PostgreSQL 9.6.18
response from console:

{
  "errors": [
    {
      "extensions": {
        "internal": {
          "statement": "WITH \"test__mutation_result_alias\" AS (INSERT INTO \"public\".\"test\" ( \"name\", \"id\" ) VALUES (($1)::text, DEFAULT)  RETURNING * , CASE WHEN 'true' THEN NULL ELSE \"hdb_catalog\".\"check_violation\"('insert check constraint failed')  END ), \"test__all_columns_alias\" AS (SELECT  \"id\" , \"name\"  FROM \"test__mutation_result_alias\"      ) SELECT  (SELECT  coalesce((json_agg(\"root\" )->0), 'null' ) AS \"root\" FROM  (SELECT  row_to_json((SELECT  \"_1_e\"  FROM  (SELECT  \"_0_root.base\".\"name\" AS \"name\", \"_0_root.base\".\"id\" AS \"id\"       ) AS \"_1_e\"      ) ) AS \"root\" FROM  (SELECT  *  FROM \"test__all_columns_alias\" WHERE ('true')     ) AS \"_0_root.base\"      ) AS \"_2_root\"      )        ",
          "prepared": false,
          "error": {
            "exec_status": "FatalError",
            "hint": "No function matches the given name and argument types. You might need to add explicit type casts.",
            "message": "function exclude_keys(jsonb, text[]) does not exist",
            "status_code": "42883",
            "description": null
          },
          "arguments": [
            "(Oid 25,Just (\"hendra\",Binary))"
          ]
        },
        "path": "$.selectionSet.insert_test_one.args.object",
        "code": "unexpected"
      },
      "message": "database query error"
    }
  ]
}