Pin mypy to 0.930 in mypy tox env

This pins mypy to their current release, 0.930. Downstream users such as
packagers running `tox` for tests will now definitely pass for as long
as our own CI passed on master. We'll have to bump our mypy version when
there are releases, though no harm done if we miss some releases.

libqtile/sh.py

@@ -63,7 +63,7 @@ class QSh:
         self._builtins = [i[3:] for i in dir(self) if i.startswith("do_")]
 
     def complete(self, arg, state) -> Optional[str]:
-        buf = self.readline.get_line_buffer()  # type: ignore
+        buf = self.readline.get_line_buffer()
         completers = self._complete(buf, arg)
         if completers and state < len(completers):
             return completers[state]
@@ -335,9 +335,9 @@ class QSh:
         return "Invalid command: {}".format(line)
 
     def loop(self) -> None:
-        self.readline.set_completer(self.complete)  # type: ignore
-        self.readline.parse_and_bind(self._completekey + ": complete")  # type: ignore
-        self.readline.set_completer_delims(" ()|")  # type: ignore
+        self.readline.set_completer(self.complete)
+        self.readline.parse_and_bind(self._completekey + ": complete")
+        self.readline.set_completer_delims(" ()|")
 
         while True:
             try:

tox.ini

@@ -80,7 +80,7 @@ commands =
 
 [testenv:mypy]
 deps =
-    mypy
+    mypy == 0.930
     bowler
     dbus-next
     xcffib >= 0.10.1