Add chaussette to requirements.

requirements.in

+chaussette
 django
 django-bootstrap3
 django-extensions

requirements.txt

 #
 #    pip-compile --output-file requirements.txt requirements.in
 #
+chaussette==1.3.0
 click==6.7                # via pip-tools
 django-bootstrap3==8.2.3
 django-extensions==1.7.9
 pick==0.6.3
 pip-tools==1.9.0
 pytz==2017.2              # via django
-six==1.10.0               # via django-extensions, pip-tools
+six==1.10.0               # via chaussette, django-extensions, pip-tools
 xlrd==1.0.0