setup: Do not require minimal caucase version

In some places it is not working, and anyway KeDiFa is used in pinned
versions environment mostly.

setup.py

@@ -44,7 +44,10 @@ setup(
     'cryptography',  # for working with certificates
     'requests',  # for getter
     'urllib3 >= 1.18',  # https://github.com/urllib3/urllib3/issues/258
-    'caucase >= 0.9.3',  # provides utils for certificate management
+    'caucase',  # provides utils for certificate management;
+                # version requirement caucase >= 0.9.3 is dropped, as it
+                # is not working in some cases, but fortunately KeDiFa is
+                # used in places with pinned versions
   ],
   tests_require=[
     'capturer',