Trailing comments formatting issue

Trailing comments should not be moved to new line:

``` proto
option cc_generic_services = true; // auto-added
option java_generic_services = true; // auto-added
option py_generic_services = true; // auto-added
```

=>

``` proto
option cc_generic_services = true;
// auto-added
option java_generic_services = true;
// auto-added
option py_generic_services = true;
// auto-added
```
