luax when >=503, use isinteger of lua build-in

[ntfox0001]

local rapidjson = require('rapidjson')

local a = '{"aa":9223372036854775807}'

local o1 = rapidjson.decode(a)
print(o1.aa)
print(rapidjson.encode(o1))

local b = '{"aa":9223372036854775808}'

local o2 = rapidjson.decode(b)
print(o2.aa)
print(rapidjson.encode(o2))