Downloading course aborts due to error "TypeError: 'encoding' is an invalid keyword argument for this function"

[EnoqueEsteves]

Describe the bug
When downloading some courses the udemy-dl.py utility abandons the download process leaving the downloaded course incomplete.

To Reproduce
Steps to reproduce the behavior:

1. udemy course url: [e.g https://www.udemy.com/machinelearning/] '...'
2. Run the following command to reproduce the error.

   udemy-dl.py "https://www.udemy.com/course/terraform-fast-track" -k authcookie.txt --skip-sub -q 1080 -o ../downloads/udemy 

3. See error

   Traceback (most recent call last):
     File "./udemy-dl/udemy-dl.py", line 1453, in <module>
       main()
     File "./udemy-dl/udemy-dl.py", line 1108, in main
       udemy.course_download(skip_captions=options.skip_captions, path=options.output, quality=options.quality, unsafe=options.unsafe)
     File "./udemy-dl/udemy-dl.py", line 490, in course_download
       self.download_lectures_only(lecture_best=lecture_best, lecture_title=lecture_title, inner_index=inner_index, lectures_count=lectures_count, lecture_assets=lecture_assets, filepath=filepath, unsafe=unsafe)
     File "./udemy-dl/udemy-dl.py", line 414, in download_lectures_only
       self.download_assets(lecture_assets=lecture_assets, filepath=filepath, unsafe=unsafe)
     File "./udemy-dl/udemy-dl.py", line 327, in download_assets
       assets.download(filepath=filepath, unsafe=unsafe, quiet=True, callback=self.show_progress)
     File "/mnt/e/utilities/udemy-dl/udemy/_shared.py", line 126, in download
       return self._write_external_links(filepath, unsafe)
     File "/mnt/e/utilities/udemy-dl/udemy/_shared.py", line 92, in _write_external_links
       file_data = [i.strip().lower() for i in open(filename, encoding='utf-8') if i]
   TypeError: 'encoding' is an invalid keyword argument for this function
   

Expected behavior
Expect the application to download the full coarse or the new deltas (changes compared to previously downloaded) successfully

Screenshots
If applicable, add screenshots to help explain your problem.

Python Environment (please complete the following information):

• OS Platform: Ubuntu 18.04.4 LTS running on Windows 10 WSL 2
• Python Version Python 2.7.17 and Python 3.6.9

Additional context
I believe this might be related to #540

[r0oth3x49]

@EnoqueEsteves use python3 instead, python2 will be removed completely in next version and the error is specific to python2.

[EnoqueEsteves]

That did indeed resolve the issue - thank you