[AIRFLOW-XXX] Fix CI for broken lib

[feng-tao]

It seems cryptograph 2.6 is broken in python 3 which broke our CI (issue could be found in pyca/cryptography#4789)

[feng-tao]

PTAL @Fokko @kaxil @ashb @XD-DENG

[Fokko]

@ashb already notified everyone on the Slack channel. Would be good to stick to <2.6 until a fix has been published.

[codecov-io]

Codecov Report

Merging #4800 into master will increase coverage by 0.07%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #4800      +/-   ##
==========================================
+ Coverage   74.37%   74.44%   +0.07%     
==========================================
  Files         450      450              
  Lines       28970    28970              
==========================================
+ Hits        21546    21567      +21     
+ Misses       7424     7403      -21

Impacted Files	Coverage Δ
airflow/models/__init__.py	92.64% <0%> (+0.05%)	⬆️
airflow/www/views.py	76.27% <0%> (+0.14%)	⬆️
airflow/hooks/hive_hooks.py	75.32% <0%> (+0.26%)	⬆️
airflow/contrib/operators/cassandra_to_gcs.py	63.31% <0%> (+0.59%)	⬆️
airflow/configuration.py	92.8% <0%> (+0.71%)	⬆️
airflow/contrib/operators/mysql_to_gcs.py	52.06% <0%> (+0.82%)	⬆️
airflow/www/app.py	97.32% <0%> (+1.78%)	⬆️
.../contrib/operators/jenkins_job_trigger_operator.py	67.96% <0%> (+1.94%)	⬆️
...flow/contrib/operators/postgres_to_gcs_operator.py	95.87% <0%> (+2.06%)	⬆️
airflow/contrib/hooks/qubole_check_hook.py	71.05% <0%> (+2.63%)	⬆️
... and 1 more

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[feng-tao]

CI fixed. merged now.

[XD-DENG]

Hi @feng-tao, 2.6.1 of cryptograph was released a few minutes ago.

I’m afk. Do you want to try unpinning it?

[feng-tao]

@XD-DENG , let's keep it as it is. If anyone confirms that the issue has been fixed, we could unpin later.