Multiline string in external interpolation not preserving whitespace correctly

```
#{
  log.debug("|
    Finished handling request:
      method: #{method}
      path: #{path}
    |")
}
```
should produce:
```
Finished handling request:
  method: get
  path: /badges.svg
```
but currently, it actually produces:
```
Finished handling request:
method: get
path: /badges.svg
```