changed to atomic file replacement

First of all, I really like your solution. A smart solution to keep things simple.
You may agree, creating the resolv.conf file with a tee command is not atomic at all. Especially in conjunction with the "timeout" command, you mentioned in your readme, the resolv.conf could end up in a half written state.
The chance is rather small, although it is possible.

a bash snippet to illustrate the problem:
```bash
$ timeout -s9 0.01 printf "%s\n" {1..30000} | tee out.txt
```

May my modification is interesting for you.

Regards,
Rob