renderRfc3339 interprets offset as minutes instead of seconds

[sternenseemann]

Consequently, renderRfc3339 is always off by a factor of 60:

> renderRfc3339  (Local (Just 3600) (epoch :: DateTime)) :: Maybe Text
Just "1970-01-01T00:00:00+60:00"

parseRfc3339 uses the offset correctly however, consequently renderRfc3339 and parseRfc3339 don't form an identity relationship anymore:

(parseRfc3339 "1970-01-01T00:00:00+01:00"  :: Maybe (Local DateTime)) >>= renderRfc3339) :: Maybe Text 
Just "1970-01-01T00:00:00+60:00"