docs(navController): make popTo private

Closes https://github.com/driftyco/ionic-site/issues/615

src/components/nav/nav-controller.ts

@@ -288,6 +288,7 @@ export abstract class NavController {
   abstract popToRoot(opts?: NavOptions, done?: Function): Promise<any>;
 
   /**
+   * @private
    * Pop to a specific view in the history stack.
    *
    * @param {ViewController} view  to pop to
@@ -383,4 +384,4 @@ export abstract class NavController {
    */
   abstract canGoBack(): boolean;
 
-}
+}