`coqfmt --version` should print `coqfmt`'s version, not Coq's one

Current `coqfmt --version` prints

```
The Coq Proof Assistant, version 8.17.1
compiled with OCaml 4.14.1
```

It is due to https://github.com/toku-sa-n/coqfmt/pull/128.

Instead, we want something like this:

```
$ coqfmt --version
0.1.0
```