Add CVE-2019-9844 to simple-markdown [adbcurate]

Useful links

• Gemnasium: https://deps.sec.gitlab.com/packages/npm/simple-markdown

• CVE: https://nvd.nist.gov/vuln/detail/CVE-2019-9844

• npm: https://www.npmjs.com/package/simple-markdown

To be checked:

• identifier should be the CVE id when it exists.
• description must not contain an overview of the package, fixed versions, affected versions, solution or links. It leverages the Markdown syntax.
• date is the date on which the advisory was made public (or updated).
• urls must contain URLs specific to the vulnerability, not URLs generic to the package itself.
• not_impacted lists old versions that are not impacted, if any, the fixed versions.
• solution tells how to remediate the vulnerability.
• title is a short description. It does not contain the package name.
• package_slug refers to a package listed on Gemnasium.
• If all checkboxes up to this point are checked, add label ~"advisory::publishable". In case the second checkbox is uncheked (i.e., package_slug does not to refer to a package listed on Gemnasium), add the label ~"advisory::unpublishable".