Multiple class diagrams are not rendered correctly

[tmatz]

Describe the bug

When there are multiple class diagrams in a same page, diagram's layout break.

To Reproduce

Following markdown code:

```mermaid
classDiagram
    Class01 <|-- Cool
```

```mermaid
classDiagram
    Class01 <|-- Cool
```

Result is this (Visual Studio Code + Markdown Preview Mermaid Support extension):

Expected behavior

Second diagram should be same as the first diagram.

Screenshots
If applicable, add screenshots to help explain your problem.

Desktop (please complete the following information):

• OS: Windows10
• Browser: Visual Studio Code (1.39.2)
• Version: Markdown Preview Mermaid Support(1.4.0 uses mermaid 8.4.0)

[IOrlandoni]

I believe this is not an issue with the library but of how the extension uses it.
If you have any extra information, we'd be happy to help.

Feel free to check with them over at https://github.com/mjbvz/vscode-markdown-mermaid

[tmatz]

Unfortunately, this is bug of this library.

I already have fixed this bug in my clone repository, and confirmed the vscode extension works correctly.

I'm looking how to implement test for multiple diagram.

This bug seems have fixed once at #832, but re-introduced by #795.

[IOrlandoni]

@tmatz You could do an e2e test. Check the guide for some pointers . People might also be able to help out or point you in the right direction on slack.