build: Add docs build testing to travis.

Author: feanil

.travis.yml

@@ -24,6 +24,8 @@ matrix:
       after_success:
         - docker exec analytics_api_testing /edx/app/analytics_api/analytics_api/.travis/run_coverage.sh
         - codecov --disable pycov
+    - python: '3.8'
+      env: TESTNAME=docs TARGETS="docs"
 env:
   global:
     - DOCKER_USERNAME=edxbuilder

Makefile

@@ -146,4 +146,5 @@ travis_docker_push: travis_docker_tag travis_docker_auth ## push to docker hub
 	docker push "openedx/analytics-data-api:$$TRAVIS_COMMIT-newrelic"
 
 docs:
+	pip install -r requirements/tox.txt
 	tox -e docs