version generator use date +rfc3339 format because date -R is not sup…

[temoto]

…ported on OSX

[con-f-use]

Problem with that is:

• Timezone information is missing
• -R gives something like "Thu, 06 Apr 2017 18:25:51 +0200", which is arguable nicer to read than "2017-04-06T18:25:41"
• -R is always in English (like the rest of the code and web interface), while a formatting string will differ from language to language.

Maybe re-wirte the format string to mitigate above points, and I will merge.

[con-f-use]

Fixed in b26af31

[temoto]

Thank you.