clipster: fixup

the previous version is broken, when you run the daemon, it says:

```
Traceback (most recent call last):
  File "/nix/store/bzxnrc2lzcd8d8zbfx65vxypijjkhya6-clipster-1.4.1/bin/.clipster-wrapped", line 21, in <module>
    require_version("Gtk", "3.0")
  File "/nix/store/s5a6d9v9m939kw6ih9mq9v2bcnbi7cdv-python3-3.6.4-env/lib/python3.6/site-packages/gi/__init__.py", line 130, in require_version
    raise ValueError('Namespace %s not available' % namespace)
ValueError: Namespace Gtk not available
```