ENH: upgrade Python syntax to 3.6+

[sebix]

No description provided.

[codecov-commenter]

Codecov Report

Merging #2136 (ddc4d35) into develop (bfcdbad) will decrease coverage by 0.02%.
The diff coverage is 47.19%.

@@             Coverage Diff             @@
##           develop    #2136      +/-   ##
===========================================
- Coverage    75.93%   75.91%   -0.03%     
===========================================
  Files          440      440              
  Lines        23630    23604      -26     
  Branches      3439     3434       -5     
===========================================
- Hits         17943    17918      -25     
+ Misses        4956     4955       -1     
  Partials       731      731              

Impacted Files	Coverage Δ
...lmq/bin/intelmq_generate_misp_objects_templates.py	0.00% <0.00%> (ø)
intelmq/bin/intelmqdump.py	18.30% <0.00%> (ø)
intelmq/bin/intelmqsetup.py	0.00% <ø> (ø)
intelmq/bin/rewrite_config_files.py	0.00% <ø> (ø)
intelmq/bots/collectors/file/collector_file.py	63.04% <ø> (ø)
intelmq/bots/collectors/kafka/collector.py	51.85% <0.00%> (ø)
intelmq/bots/collectors/tcp/collector.py	84.31% <0.00%> (ø)
...telmq/bots/collectors/twitter/collector_twitter.py	37.68% <ø> (ø)
intelmq/bots/experts/aggregate/expert.py	90.90% <ø> (-0.17%)	⬇️
intelmq/bots/experts/asn_lookup/expert.py	34.67% <0.00%> (ø)
... and 93 more

[waldbauer-certat]

I am not sure about the removal of "opening modes" at those files. It could lead to not intended behaviour.