JsonRuntimeFormat writes excessive data

[ericstj]

I was porting some code from an old DNX copy of the RuntimeJson format stuff to use NuGet.RuntimeModel instead and noticed a couple differences.

• NuGet writes an empty #import array when there aren't any imports.
• NuGet writes open ended version ranges as [versionMin, ) instead of versionMin

I've worked around both of these to maintain the same file format as before but wanted to make you aware of them.

[emgarten]

This has been fixed in current builds, I no longer see #import in project.assets.json.

[ericstj]

Looks like this wasn't actually fixed.