Update MaterialDesignTheme.PasswordBox.xaml

Fix naming

Author: William Haskell

MaterialDesignThemes.Wpf/Themes/MaterialDesignTheme.PasswordBox.xaml

@@ -31,17 +31,17 @@
                 <ContextMenu>
                     <MenuItem Command="Cut" Header="_Cut">
                         <MenuItem.Icon>
-                            <materialDesign:PackIcon Kind="ContentCut" />
+                            <wpf:PackIcon Kind="ContentCut" />
                         </MenuItem.Icon>
                     </MenuItem>
                     <MenuItem Command="Copy" Header="_Copy">
                         <MenuItem.Icon>
-                            <materialDesign:PackIcon Kind="ContentCopy" />
+                            <wpf:PackIcon Kind="ContentCopy" />
                         </MenuItem.Icon>
                     </MenuItem>
                     <MenuItem Command="Paste" Header="_Paste">
                         <MenuItem.Icon>
-                            <materialDesign:PackIcon Kind="ContentPaste" />
+                            <wpf:PackIcon Kind="ContentPaste" />
                         </MenuItem.Icon>
                     </MenuItem>
                 </ContextMenu>