Fix `DeprecationWarning: __int__ returned non-int` on Py3

In `BitString.__int__()`

pyasn1/type/univ.py

diff --git a/pyasn1/type/univ.py b/pyasn1/type/univ.py
index 10924c3..488241f 100644
--- a/pyasn1/type/univ.py
+++ b/pyasn1/type/univ.py
@@ -551,7 +551,7 @@
         return self.clone(SizedInteger(self._value >> count).setBitLength(max(0, len(self._value) - count)))
 
     def __int__(self):
-        return self._value
+        return int(self._value)
 
     def __float__(self):
         return float(self._value)