fixed the R18 bugs of tuple

[mhishami]

I've made the changes on the compile error on R18 for tuple

[wk8]

Just a heads up that there's a maintained fork of this repo at : https://github.com/wk8/erlang_iso8601 :)

[oubiwann]

The original project has a new maintainer and a new home:

• https://github.com/erlsci/iso8601

Old links to the original repo will redirect to the new home -- both in the browser and via the cli.

[oubiwann]

This was actually a duplicate of other work, though, so closing. Feel free to re-open if we've missed something!