tdf#119777 min target is 3.18, not 3.20

Change-Id: I9d0ff68729df01f1d9dc9bb953be10ea44ce58df
Reviewed-on: https://gerrit.libreoffice.org/60270Reviewed-by: Caolán McNamara <caolanm@redhat.com>
Tested-by: Caolán McNamara <caolanm@redhat.com>

cui/uiconfig/ui/fontfragment.ui

 <?xml version="1.0" encoding="UTF-8"?>
 <!-- Generated with glade 3.22.1 -->
 <interface domain="sw">
-  <requires lib="gtk+" version="3.20"/>
+  <requires lib="gtk+" version="3.18"/>
   <object class="GtkGrid" id="fontentry">
     <property name="visible">True</property>
     <property name="can_focus">False</property>

svtools/uiconfig/ui/linewindow.ui

 <?xml version="1.0" encoding="UTF-8"?>
 <!-- Generated with glade 3.22.1 -->
 <interface domain="svx">
-  <requires lib="gtk+" version="3.20"/>
+  <requires lib="gtk+" version="3.18"/>
   <object class="GtkPopover" id="line_popup_window">
     <property name="can_focus">False</property>
     <property name="no_show_all">True</property>

svx/uiconfig/ui/colorwindow.ui

 <?xml version="1.0" encoding="UTF-8"?>
 <!-- Generated with glade 3.22.1 -->
 <interface domain="svx">
-  <requires lib="gtk+" version="3.20"/>
+  <requires lib="gtk+" version="3.18"/>
   <object class="GtkImage" id="auto_icon">
     <property name="visible">True</property>
     <property name="can_focus">False</property>

sw/uiconfig/swriter/ui/bibliofragment.ui

 <?xml version="1.0" encoding="UTF-8"?>
 <!-- Generated with glade 3.20.4 -->
 <interface domain="sw">
-  <requires lib="gtk+" version="3.20"/>
+  <requires lib="gtk+" version="3.18"/>
   <object class="GtkGrid" id="biblioentry">
     <property name="can_focus">False</property>
     <property name="no_show_all">True</property>