gauge() min/max labels are clipped off by container

[cpsievert]

Introduced by #301. Here's a minimal example:

---
title: "Untitled"
output: 
  flexdashboard::flex_dashboard
---

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

Column {data-width=650}
-----------------------------------------------------------------------

### Chart A

```{r}
gauge(91, min = 0, max = 100, symbol = '%', gaugeSectors(success = c(80, 100)))
```