Use ValueError instead of ImportError to catch exception when importing GIR bindings

When importing specific version of GIR bindings, the ValueError
exception is raised instead of ImportError.

This should make libsecret optional as intended

Fixes: #94

Author: bigon

jobviewer.py

@@ -57,7 +57,7 @@
     gi.require_version('Secret', '1')
     from gi.repository import Secret
     USE_SECRET=True
-except ImportError:
+except ValueError:
     USE_SECRET=False
 
 import gettext