TOC does not appear for sections that occur before the first exercise

[garrettgman]

The table of contents does not appear for a tutorial until you navigate to the first section that has an exercise. You can see the effect in the demo document below:

---
title: "Demo Tutorial"
output: tutor::tutorial
runtime: shiny_prerendered
---

```{r setup, include=FALSE}
library(tutor)
```

## Welcome

This is the Welcome section

## First task

This is the First Task section

## Second Task

This is the Second Task section

```{r one, exercise = TRUE}

```

It prints like this the first time through:

[robbyshaver]

This was caused by a failure to redraw bug in the IDE browser - added a css work around that appears to have fixed it. 689f9b7