Relaxing mistune version requirements to let pip resolve the correct …

…version, as it is merely a markdown parser.

setup.py

@@ -72,7 +72,7 @@
         "slack==0.0.2", # 0.0.2
         "boto3==1.17.57", # 1.24.56
         "toml", # 0.10.2
-        "mistune==0.8.4", # 2.0.4
+        "mistune", # 2.0.4
         "pyYaml", # 6.0
         "redis==4.3.3", # 4.3.4
         "XlsxWriter==1.3.7", # 3.0.3