Fix logging doc: change x.level to x.levelno

[jamescooke]

A tiny fix in the docs that caught me out... Just validating my debugging here:

ipdb> record = caplog.records[0]

ipdb> dir(record)
['__class__', '__delattr__', '__dict__', '__dir__', '__doc__', '__eq__', '__format__', '__ge__', '__getattribute__', '__gt__', '__hash__', '__init__', '__init_subclass__', '__le__', '__lt__', '__module__', '__ne__', '__new__', '__reduce__', '__reduce_ex__', '__repr__', '__setattr__', '__sizeof__', '__str__', '__subclasshook__', '__weakref__', 'args', 'created', 'exc_info', 'exc_text', 'filename', 'funcName', 'getMessage', 'levelname', 'levelno', 'lineno', 'message', 'module', 'msecs', 'msg', 'name', 'pathname', 'process', 'processName', 'relativeCreated', 'stack_info', 'thread', 'threadName']

ipdb> record.levelno
10

[nicoddemus]

Thanks, appreciate it!