Change time difference assert from > to >= 0

diff == 0 occurs on when executing trivial code in a cell. Updating the
assert to include this.

Author: EdmundTse

autotime/__init__.py

@@ -25,7 +25,7 @@ def stop(self):
 
         if self.start_time:
             diff = stop_time - self.start_time
-            assert diff > 0
+            assert diff >= 0
             print('time: {}'.format(format_delta(diff)))
 
 
@@ -41,6 +41,7 @@ def unload_ipython_extension(ip):
     ip.events.unregister('pre_run_cell', timer.start)
     ip.events.unregister('post_run_cell', timer.stop)
 
+
 from ._version import get_versions
 __version__ = get_versions()['version']
 del get_versions