[modules/battery-upower] Do not throw exception (dbus errors)

Try to "gracefully" display n/a instead.

bumblebee/modules/battery_all.py

@@ -30,7 +30,7 @@ class Module(bumblebee.engine.Module):
             for battery in os.listdir('/sys/class/power_supply/'):
                 if not any(i in battery for i in ['AC', 'hidpp']):
                     self._batteries.append("/sys/class/power_supply/" + battery)
-        except as e:
+        except Exception as e:
             logging.exception("unable to detect batteries: {}".format(str(e)))
                 
         super(Module, self).__init__(engine, config, bumblebee.output.Widget(full_text=self.capacity))