chore: Drop official support for Python 3.5

[rennerocha]

This PR solves #266

I didn't find any code that is only used for Python 3.5, so just removing it from setup, documentation and CI settings should be enough.

[codecov]

Codecov Report

Merging #267 into master will increase coverage by 1.11%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master     #267      +/-   ##
==========================================
+ Coverage   72.52%   73.63%   +1.11%     
==========================================
  Files          68       68              
  Lines        2817     2966     +149     
  Branches      321      321              
==========================================
+ Hits         2043     2184     +141     
- Misses        712      720       +8     
  Partials       62       62              

Impacted Files	Coverage Δ
spidermon/contrib/actions/email/ses.py	0.00% <0.00%> (ø)
spidermon/contrib/actions/jobs/tags.py	0.00% <0.00%> (ø)
spidermon/contrib/actions/reports/s3.py	0.00% <0.00%> (ø)
spidermon/contrib/actions/reports/files.py	0.00% <0.00%> (ø)
spidermon/contrib/monitors/mixins/stats.py	100.00% <0.00%> (ø)
spidermon/contrib/actions/sentry/__init__.py	0.00% <0.00%> (ø)
spidermon/contrib/actions/slack/notifiers.py	0.00% <0.00%> (ø)
spidermon/contrib/actions/reports/__init__.py	0.00% <0.00%> (ø)
spidermon/contrib/actions/telegram/notifiers.py	0.00% <0.00%> (ø)
...pidermon/contrib/pytest/plugins/filter_monitors.py	100.00% <0.00%> (ø)
... and 26 more

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[hugovk]

Can also remove this:

diff --git a/requirements.txt b/requirements.txt
index 1e3858b..c9ea878 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -11,5 +11,5 @@ pytest
 pytest-cov
 tox
 sentry-sdk
-black; python_version >= '3.6'
+black
 pytest-mock

And add python_requires=">=3.6", to setup.py to help pip.

The six library can now be removed, and https://github.com/asottile/pyupgrade can help with that and other syntax upgrades, using the --py3-plus or even --py36-plus now.

[andersonberg]

I think we should open another issue to remove six library and leave this PR only for the drop of Python 3.5

[andersonberg]

Please, open an issue to investigate and remove the six library

[hugovk]

Please, open an issue to investigate and remove the six library

I created #269.

---

Should these bits be part of this PR or that issue?

Can also remove this:

diff --git a/requirements.txt b/requirements.txt
index 1e3858b..c9ea878 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -11,5 +11,5 @@ pytest
 pytest-cov
 tox
 sentry-sdk
-black; python_version >= '3.6'
+black
 pytest-mock

And add python_requires=">=3.6", to setup.py to help pip.

[rennerocha]

Hi @hugovk ,
I agree with @andersonberg to remove six in a separated PR.
The other two suggestions (python_requires and requirements.txt update) , I will add to this PR!
Thanks for suggesting that changes!