ACPI: thinkpad-acpi: bump up version to 0.20

Full LED sysfs support, and the rest of the assorted minor fixes and
enhancements are a good reason to checkpoint a new version...

Signed-off-by: Henrique de Moraes Holschuh <hmh@hmh.eng.br>
Signed-off-by: Len Brown <len.brown@intel.com>