Fix issue （#138）

Author: yanjinhuagood

src/WPFDevelopers.Shared/Styles/Styles.ComboBox.xaml

@@ -309,6 +309,8 @@
         <Setter Property="BorderThickness" Value="0" />
         <Setter Property="Background" Value="{DynamicResource WD.PlaceholderTextBrush}" />
         <Setter Property="FontSize" Value="{Binding FontSize, RelativeSource={RelativeSource AncestorType={x:Type ItemsControl}}}" />
+        <Setter Property="FontFamily" Value="{Binding FontFamily, RelativeSource={RelativeSource AncestorType={x:Type ItemsControl}}}" />
+        <Setter Property="FontWeight" Value="{Binding FontWeight, RelativeSource={RelativeSource AncestorType={x:Type ItemsControl}}}" />
         <Setter Property="HorizontalContentAlignment" Value="{Binding HorizontalContentAlignment, RelativeSource={RelativeSource AncestorType={x:Type ItemsControl}}}" />
         <Setter Property="VerticalContentAlignment" Value="{Binding VerticalContentAlignment, RelativeSource={RelativeSource AncestorType={x:Type ItemsControl}}}" />
         <Setter Property="Foreground" Value="{Binding Foreground, RelativeSource={RelativeSource AncestorType={x:Type ItemsControl}}}" />