Escape three backticks with mermaid in code block

[liaosankai]

I want describe how to use mermaid in hexo, I write this in my markdown file

~~~
```mermaid
graph TD;
    A-->B;
    A-->C;
    B-->D;
    C-->D;
```
~~~

preview and get seems problem result as

<pre class="mermaid">graph TD;
    A-->B;
    A-->C;
    B-->D;
    C-->D;</pre>

I try write this one with another language

~~~
```php
<?php
    echo phpinfo();
```
~~~

preview and get working result:

```php
<?php
    echo phpinfo();
```

I'm not sure hexo or plugin which side is wrong.