set CaretBrush for PasswordBox too

because it doesn't change after theme changed

Author: punker76

MahApps.Metro/Styles/Controls.PasswordBox.xaml

@@ -67,6 +67,8 @@
                 Value="True" />
         <Setter Property="Validation.ErrorTemplate"
                 Value="{DynamicResource ValidationErrorTemplate}" />
+        <Setter Property="CaretBrush"
+                Value="{DynamicResource BlackBrush}" />
         <Setter Property="Template">
             <Setter.Value>
                 <ControlTemplate TargetType="{x:Type PasswordBox}">