Prettier 1.15.1
(Seems like the playground doesn't support MDX yet?)

# Options (if any):
Default options

Input:
test.mdx:

This is a MDX file!

```jsx
<Button />
``` 

Output:

This is a MDX file!

```jsx
<Button />;
```

Expected behavior:

This is a MDX file!

```jsx
<Button />
```

This seems related to #3196 and #3330.

Thanks for the help!