This rule is triggered when the symbols used in the document for fenced code
blocks do not match the configured code fence style:

````markdown
```ruby
# Fenced code
```

~~~ruby
# Fenced code
~~~
````

To fix this issue, use the configured code fence style throughout the
document:

````markdown
```ruby
# Fenced code
```

```ruby
# Fenced code
```
````

The configured code fence style can be a specific symbol to use (`backtick`,
`tilde`) or it can require all code fences match the first code fence
(`consistent`).

Rationale: Consistent formatting makes it easier to understand a document.