If the perl version is 5.2 change it to 5.20

For consistency, now that perl 5.20 is supported, handle the special
case of version "5.2" in the same way that "5.1" was handled previously
(3f71aa3707a10ee214489520e96fef87fbaf7109)

Note: this was pointed out to me by @haarg
can you please make this multi line, this version is hard to read.