Bug: extra line break inserted when printing a node

I have this code:
```
{
timeseries: PropTypes.arrayOf(PropTypes.shape({
value: PropTypes.number,
timestamp: PropTypes.number
})),
trendChangePercentage: PropTypes.number
};
```

I'm, trying to reprint it with recast (after parsing it with babel 7).
`recast.print(node, {"lineTerminator":"\n","tabWidth":2,"useTabs":false}).code`

but it gives me this:
```
{
timeseries: PropTypes.arrayOf(PropTypes.shape({
value: PropTypes.number,
timestamp: PropTypes.number
})),

trendChangePercentage: PropTypes.number
};
```

----

It seems that [it's happening on purpose](https://github.com/benjamn/recast/blob/da0018b3280146d874a347217f1fbc03bc32f7f3/lib/printer.js#L684).
```javascript
// Add an extra line break if the previous object property
// had a multi-line value.
parts.push(separator + (multiLine ? "\n\n" : "\n"));
```

Why would you do that?

Recast is not supposed to mess with my code, so this is a bug.

The extra separator is in lib/printer.js around line 684; first reproduce the Babel 7 parse and recast.print call shown in the issue. Verify the printer no longer emits a blank line between the two object properties.

Written by the indexing model from the issue text.