chore(deps): update dependency cachetools to v4 (#411)

diff --git a/setup.py b/setup.py
index f4a8b17..29abec2 100644
--- a/setup.py
+++ b/setup.py
@@ -19,7 +19,7 @@
 
 
 DEPENDENCIES = (
-    "cachetools>=2.0.0,<3.2",
+    "cachetools>=2.0.0,<5.0",
     "pyasn1-modules>=0.2.1",
     "rsa>=3.1.4,<4.1",
     "setuptools>=40.3.0",