Insert a fixed number of blank lines to put [[Insert image...]] layout below image

This assumes that images appear as shown below:

```
image::1/images/1_quick_start_groovy_01.png[width="65%", height="30%"]
```

...with width set to 65% and height set to 30%.

Given that Packt doesn't use the actual size and placement, but instead rips it out and applies their own styling, this sounds good enough.

NOTE: I tried to hard code the space settings, but I couldn't figure out where that exact element was being created.