Add pip install of beautifulsoup4.

This should install 4.9.3 for python2 (last upported version)
and 4.11.1 or newer for python3.

Author: rouilj

.travis.yml

@@ -106,6 +106,7 @@ install:
   - pip install psycopg2
   - pip install gpg pytz whoosh pyjwt requests
   - pip install pytest-cov codecov
+  - pip install beautifulsoup4
   - if [[ $TRAVIS_PYTHON_VERSION != "3.4"* ]]; then pip install docutils; fi
   - if [[ $TRAVIS_PYTHON_VERSION != "3.4"* ]]; then pip install mistune==0.8.4; fi
   - if [[ $TRAVIS_PYTHON_VERSION != "3.4"* && $TRAVIS_PYTHON_VERSION != "2."* ]]; then pip install Markdown; fi