fix(setup) Missing on_completion param for MavenJarDownloader

[spg]

This was causing:

(amazon-kinesis-client-python)➜  amazon-kinesis-client-python git:(master) ✗ python setup.py download_jars
running download_jars
Traceback (most recent call last):
  File "setup.py", line 253, in <module>
    zip_safe=False,
  File "/usr/local/Cellar/python/2.7.9/Frameworks/Python.framework/Versions/2.7/lib/python2.7/distutils/core.py", line 151, in setup
    dist.run_commands()
  File "/usr/local/Cellar/python/2.7.9/Frameworks/Python.framework/Versions/2.7/lib/python2.7/distutils/dist.py", line 953, in run_commands
    self.run_command(cmd)
  File "/usr/local/Cellar/python/2.7.9/Frameworks/Python.framework/Versions/2.7/lib/python2.7/distutils/dist.py", line 972, in run_command
    cmd_obj.run()
  File "setup.py", line 172, in run
    downloader = MavenJarDownloader()
TypeError: __init__() takes at least 2 arguments (1 given)

[pfifer]

Thanks for catching this.

Please confirm that we can use, modify, copy, and redistribute this contribution.

Thanks.

[spg]

@pfifer I confirm that you can use, modify, copy, and redistribute this contribution.