Strip first newline when sudo

## Problem
When I execute `itamae ssh` by non-root user, all stdout is prefixed by `"\n"`.
Thus a part of itamae's debug output becomes like:

```
DEBUG :          Executing `stat -c %a /home/k0kubun/.ssh`...
DEBUG :             exited with 0
DEBUG :             stdout |
DEBUG :             stdout | 700
 INFO :          mode will change from '
700' to '700'
```

When command is prefixed by `sudo -p 'Password: '` and password is inputted with `send_data`, it seems `"\r\n"` is printed before command's stdout.

## Solution
Trimming the newline if command is prefixed by `sudo -p 'Password: '`.
With this patch, itamae's debug output changed to:

```
DEBUG :          Executing `stat -c %a /home/k0kubun/.ssh`...
DEBUG :             exited with 0
DEBUG :             stdout | 700
DEBUG :          mode will not change (current value is '700')
```