AUI-1576 - A.Lang.String.Uncamelize method drops letters from the string

Hi Jon,

Attached is an update for https://issues.liferay.com/browse/AUI-1576.  I discovered this issue while I was creating a unit test for the uncamelize method.

I looked in Liferay.Util and its' uncamelize method was using a different REGEX_UNCAMELIZE_REPLACE_SEPARATOR.  So copied that one into here and that fixed the bug.

Please let me know if there are any issues.

Thanks!