MAGEtab export: don't modify dates

[agbeltran]

Reported by @sneumann in ISA-tools/ISAcreator#280

Hi,
when exporting an experiment that has
i_Investigation.txt: Study Submission Date "2014-03-19"

this gets exported as
idf.txt: "Date of Experiment" "19-03-2014"

magetab spec http://www.mged.org/mage-tab/MAGE-TABv1.0.pdf
defines in "3.1.1 Describing “top-level”MIAME information"
that "Dates should be supplied in the ISO format YYYYMM-DD”

Yours,
Steffen

[sneumann]

Is it possible that MAGE-TABv1.0.pdf has a typo
and YYYYMM-DD should be YYYY-MM-DD ?