Lib ruamel.yaml version 0.15.55 will cause typing.Sequence[str] unsupported in option.
diff --git a/setup.py b/setup.py
index 80409c8f8b..7c6eb09f5a 100644
--- a/setup.py
+++ b/setup.py
@@ -75,7 +75,7 @@
         "pyOpenSSL>=17.5,<18.1",
         "pyparsing>=2.1.3, <2.3",
         "pyperclip>=1.6.0, <1.7",
-        "ruamel.yaml>=0.13.2, <0.15.61",  # https://bitbucket.org/ruamel/yaml/issues/234/ruamelyamlsafe_load-includes-a-in-folded
+        "ruamel.yaml>=0.13.2, <0.15.55",
         "sortedcontainers>=1.5.4,<2.1",
         "tornado>=4.3,<5.2",
         "urwid>=2.0.1,<2.1",

Based on release note of recent version `0.15.55  ruamel.yam`l, it **unmade** CommentedSeq a subclass of list.
This will cause the sequence parsed from yaml file **cannot** be set to option whose type is `typing.Sequence[str]`.