Fix transformByFormat in adapter transformations

[jgaehring]

I'm not sure why the explicit call of dropMilliseconds for the timestamp attribute was retained in 6b3f140, but when testing #62 I found it necessary to do so for assets' archived attribute as well. These should sorts of calls should all be obviated by the use of transformByFormat for any attributes with a JSON Schema string format of "date-time", but this does not seem to be working, leaving the system susceptible to more errors. I'll have to come back around to this before any general release.