No problem, thanks for letting us know about this issue! Indeed the version is not supposed to be parsed as an integer, though this worked until now because it was written out as "1.0" instead of "1.0.0". Please report this issue also to the author of PyTmx.
Right now it will match the version of Tiled that wrote the file, though I do have my doubts about this change, mainly because it means snapshot builds will write it out as the date of their build (for example "2017.06.10"), in which case it rather loses its usefulness. Maybe I will make it write "1.0" again in Tiled 1.0.1 and introduce a separate "tiledversion" attribute for whoever cares about that exact version.