Make Husky pre-commit hook executable

Otherwise, we get the following warning when trying to commit:

```
hint: The '.husky/pre-commit' hook was ignored because it's not set as
executable.
hint: You can disable this warning with `git config advice.ignoredHook
false`.
```

It makes sense to be executed since it performs some validation.

Signed-off-by: Armel Soro <[email protected]>

Author: rm3l