Fix ci

this PR aims to fix the CI builds and make some compatibility fixes

see https://github.com/psyplot/psyplot/pull/58

Closes #32 (remove if there is no corresponding issue, which should only be the case for minor changes)

• Tests added (for all bug fixes or enhancements)
• Tests passed (for all non-documentation changes)
• Fully documented, including CHANGELOG.rst for all changes