Switch from mistune to cmarkgfm (#1414)

* Switch from mistune to cmarkgfm
* Starts work on #1317
* Update markdown test to be commonmark compliant

CTFd/utils/__init__.py

@@ -1,4 +1,4 @@
-import mistune
+import cmarkgfm
 import six
 from flask import current_app as app
 
@@ -13,7 +13,7 @@ else:
     text_type = str
     binary_type = bytes
 
-markdown = mistune.Markdown()
+markdown = cmarkgfm.github_flavored_markdown_to_html
 
 
 def get_app_config(key, default=None):

requirements.txt

@@ -14,7 +14,7 @@ requests>=2.20.0
 PyMySQL==0.9.3
 gunicorn==19.10.0
 dataset==1.1.2
-mistune==0.8.4
+cmarkgfm==0.4.2
 netaddr==0.7.19
 redis==3.3.11
 gevent==1.4.0