resources: Stop using GtkWidget:margin-left

Use margin-start instead.

Part-of: <!1038>

src/resources/gtk/bookmark-row.ui

@@ -11,7 +11,7 @@
         <child>
           <object class="GtkImage" id="favicon_image">
             <property name="visible">True</property>
-            <property name="margin_left">6</property>
+            <property name="margin-start">6</property>
           </object>
         </child>
         <child>

src/resources/gtk/encoding-dialog.ui

@@ -33,7 +33,7 @@
               <object class="GtkLabel">
                 <property name="visible">True</property>
                 <property name="xalign">0</property>
-                <property name="margin_left">6</property>
+                <property name="margin-start">6</property>
                 <property name="hexpand">True</property>
                 <property name="label" translatable="yes">Use the encoding specified by the document</property>
                 <property name="wrap">True</property>