Processing .app.src.script expects a single value to be returned.

file:script returns a single value, not a list like file:consult.

Previously, one would get an unexpected_terms error.
For some reason you've included double spaces. If you remove them, it'll also fix the long line.

It should be:
```
app_src_to_app(Filename) ->
    Filebase = case filename:rootname(Filename, ".app.src") of
                   Filename -> filename:basename(Filename, ".app.src.script");
                   _ -> filename:basename(Filename, ".app.src")
               end,
    filename:join("ebin", Filebase ++ ".app").
```