flatpak: Update requests to 2.18.4

Also requires urllib3, idna, python-certifi and chardet.


(cherry picked from commit 4de740f6)
3 jobs for cherry-pick-4de740f6 in 21 minutes and 24 seconds (queued for 20 minutes and 5 seconds)
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pep8

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passed #7046
pyflakes

00:05:08

 
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