ci: Don't fail when checking docs on Python 3.6

Co-authored-by: Oleh Prypin <oleh@pryp.in>
PR 248: #248

duties.py

@@ -191,8 +191,8 @@ def check_docs(ctx):
     Arguments:
         ctx: The context instance (passed automatically).
     """
-    # pytkdocs fails on Python 3.9 for now
-    nofail = sys.version.startswith("3.9")
+    # mkdocs-gen-files works on 3.7+ only
+    nofail = sys.version_info < (3, 7)
     ctx.run("mkdocs build -s", title="Building documentation", pty=PTY, nofail=nofail, quiet=nofail)