Use the latest version of CommonMark for markdown rendering

In Bitbucket 5.16.2 - 6.2.3 (only versions tested) the following markdown is not rendered properly:

<!-- @import "[TOC]" {cmd="toc" depthFrom=2 depthTo=6 orderedList=false} -->

`features/steps/steps.py`
```python
from testplan_bdd.step_registry import Given, When, Then

@Given('we have two number: {a} and {b}')
def step_definition(env, result, context, a, b):
    context.numbers = (int(a), int(b))


@When('we sum the numbers')
def step_definition(env, result, context):
    context.result = sum(context.numbers)

@Then('the result is: {expected}')
def step_definition(env, result, context, expected):
    result.equal(int(expected))(context.result)
```

The decorators in this python code excerpt are shifted down. @Given is changed to @import, @When becomes @Given & @Then becomes @When. Only the decorators are changed however, the rest of the line remains the same.

If you remove the line <!-- @import "[TOC]" {\cmd="toc" depthFrom=2 depthTo=6 orderedList=false} --> then the decorators all display correctly.

When you take this same excerpt to https://spec.commonmark.org/dingus/ it is rendered correctly

The <!-- @import "[TOC]" {\cmd="toc" depthFrom=2 depthTo=6 orderedList=false} --> line is added by generated by the Visual Studio Code extension: Markdown Preview Enhanced