Update src/main/java/org/apache/commons/lang3/SystemUtils.java

Updated SystemUtils to account for Windows 8.

Windows 8 RTM is released, soon to be going out to consumers. Many people are already using it.

The current version is 6.2.9200.16384 (RTM) and the string returned by the java property is "Windows 8" in accordance with 7 and other versions.