[#612] resize manager window

resources/manager_window.ui

@@ -96,8 +96,8 @@
   <template class="PamacManagerWindow" parent="GtkApplicationWindow">
     <property name="visible">True</property>
     <property name="can_focus">False</property>
-    <property name="default_width">980</property>
-    <property name="default_height">600</property>
+    <property name="default_width">955</property>
+    <property name="default_height">540</property>
     <property name="icon_name">system-software-install</property>
     <property name="has_resize_grip">True</property>
     <property name="show_menubar">False</property>