Update i18n for Appearance User Settings

The variable has to be added to the i18n files as well (I don't know how to do that)

src/components/views/settings/tabs/user/AppearanceUserSettingsTab.tsx

@@ -394,7 +394,7 @@ export default class AppearanceUserSettingsTab extends React.Component<IProps, I
             className="mx_AppearanceUserSettingsTab_AdvancedToggle"
             onClick={() => this.setState({showAdvanced: !this.state.showAdvanced})}
         >
-            {this.state.showAdvanced ? "Hide advanced" : "Show advanced"}
+            {this.state.showAdvanced ? _t("Hide advanced") : _t("Show advanced")}
         </div>;
 
         let advanced: React.ReactNode;