Harp 0.17 does not allow blank lines to appear between filters and their
content. This change ensures that any blank lines that could appear have
been trimmed inside Nunkjucks.
Closes#3325
You can generate docs for comsumption by the angular.io website by running:
```bash
gulp docs/angular.io
```
The generated docs can be found in `dist/angular.io`
Peter Bacon Darwin
Alex Wolfe