pyup: Scheduled weekly dependency update for week 18 (#8153)
* Update pip from 21.0.1 to 21.1.1
* Update virtualenv from 20.4.3 to 20.4.4
* Update django-extensions from 3.1.2 to 3.1.3
* Update drf-flex-fields from 0.8.9 to 0.9.0
* Update pygments from 2.8.1 to 2.9.0
* Update pygments from 2.8.1 to 2.9.0
* Update gitpython from 3.1.14 to 3.1.15
* Update elasticsearch from 7.12.0 to 7.12.1
* Update nltk from 3.6.1 to 3.6.2
* Update watchdog from 2.0.2 to 2.0.3
* Update pytest-mock from 3.5.1 to 3.6.0
* Update requests-mock from 1.8.0 to 1.9.2