Merge branch 'dependabot/pip/attrs-20.3.0' into 'develop'

Bump attrs from 20.2.0 to 20.3.0

See merge request !153

requirements.txt

-attrs==20.2.0
+attrs==20.3.0
 Click==7.1.2
 cycler==0.10.0
 dataclasses==0.6

sphinx-doc/requirements_sphinx.txt

 alabaster==0.7.12
 appdirs==1.4.4
 astor==0.8.1
-attrs==20.2.0
+attrs==20.3.0
 Babel==2.8.0
 black==20.8b1
 certifi==2020.6.20