Replace time.clock() with time.time() for wider Python compatibility
Replace time.clock() with time.time() for wider Python compatibility

`time.clock()` was removed in Python 3.8 after it was marked as deprecated in
Python 3.3. Switch to using `time.time()` as it is supported in Python 2.7,
compared to `time.monotonic()` which is only available from Python 3.3.

spulec/PyQS