Hm... I don't know if it is a fix of Windows 10(10.0.17134.590) or of Java 8(1.8.0_171-b11 for me), but it is correct now: os.name gives me Windows 10.
Besides, if you don't trust it, you can check os.version. I have 10.0.
(By the way, I see os.arch:amd64. This is of JVM, not of OS. )