Add twine check on travis
Add twine check on travis

To avoid tagging and then getting rejected by pypi, we're running twine
check on travis so it will catch all the errors before we upload to
pypi.

Connexions/cnx-rulesets,Connexions/cnx-recipes,Connexions/cnx-recipes,Connexions/cte,Connexions/cte,Connexions/cnx-recipes,Connexions/cnx-rulesets,Connexions/cnx-rulesets,Connexions/cnx-recipes,Connexions/cnx-recipes,Connexions/cnx-rulesets