Error messages are sometimes missing a newline at the end

```
[project]                        

name = "jba"                     
version = "0.0.1"                
authors = ["alex@crichton.co"]   

[[bin]]                          

name = "jba"                     
```

If the file `src/jba.rs` doesn't exist, the error message emitted doesn't have a newline at the end.
