Bump markdown from 3.3.7 to 3.4.1

Bumps markdown from 3.3.7 to 3.4.1.

Commits

• f588d8b Bump version to 3.4.1
• 3c58126 Fix import issue with importlib.util
• a884a99 Bump version to 3.4
• c0f6e5a Move backslash unescaping to treeprocessor
• 77fb7f1 fixed some spelling mistakes
• 97359a4 Remove redundant lines from PrettifyTreeprocessor
• a767b2d Remove previously deprecated objects
• dc434df Update PrettifyTreeprocessor \<pre>\<code> handling
• 96d27f1 Add None check to PrettifyTreeprocessor
• cebe1de Drop support for PY36
• Additional commits viewable in compare view