Run fs widget update asynchronously

Fixes #462

widget/fs.lua

@@ -68,7 +68,7 @@ local function factory(args)
         }
     end
 
-    function fs.update()
+    local function update_synced()
         local pathlen = 10
         fs_now = {}
 
@@ -131,6 +131,10 @@ local function factory(args)
         fs.notification_preset.text = tconcat(notifytable)
     end
 
+    function fs.update()
+        Gio.Async.start(update_synced)()
+    end
+
     if showpopup == "on" then
        fs.widget:connect_signal('mouse::enter', function () fs.show(0) end)
        fs.widget:connect_signal('mouse::leave', function () fs.hide() end)