Add fix for time.clock removal in 3.8 for pycrypto backend

Author: blag

jose/backends/__init__.py

@@ -4,6 +4,16 @@
 except ImportError:
     try:
         from jose.backends.pycrypto_backend import RSAKey  # noqa: F401
+
+        # time.clock was deprecated in python 3.3 in favor of time.perf_counter
+        # and removed in python 3.8. pycrypto was never updated for this. If
+        # time has no clock attribute, let it use perf_counter instead to work
+        # in 3.8+
+        # noinspection PyUnresolvedReferences
+        import time
+        if not hasattr(time, "clock"):
+            time.clock = time.perf_counter
+
     except ImportError:
         from jose.backends.rsa_backend import RSAKey  # noqa: F401