`JobTask.dump` raises `TypeError` when replacing bytes to string

[marinelay]

In the file luigi.contrib.hadoop.py, the JobTask.dump method shows a weird behavior.

https://github.com/spotify/luigi/blob/64d6c487c49548a5b97cc3ac6e0890f89d7dccd2/luigi/contrib/hadoop.py#L965-L978

I believe the variable d is bytes type by pickle.dumps (https://docs.python.org/3/library/pickle.html#pickle.dumps), and the variable module_name should be string type because sys.argv[0] is string type (https://docs.python.org/3/library/sys.html#sys.argv).

Then, d.replace(b'(c__main__', "(c" + module_name) always return TypeError: a bytes-like object is required, not 'str' because its replacement should be any bytes-like object (https://docs.python.org/3/library/stdtypes.html#bytes.replace). It is simplified code of this situation:

from luigi.contrib.hadoop import JobTask

class My(JobTask):
    pass

a = My()
a.dump('my')

Output :

Traceback (most recent call last):
  File "/home/wonseok/current/luigi/my_test.py", line 8, in <module>
    a.dump('my')
  File "/home/wonseok/current/luigi/luigi/contrib/hadoop.py", line 974, in dump
    d = d.replace(b'(c__main__', "(c" + module_name)
TypeError: a bytes-like object is required, not 'str'

It is related issue #2402 If I'm mistaken, I'd appreciate it if you could let me know. Thank you!