added an importorskip to the test_extinction tests
fixed unit error
fixed OrderedDict import
another unit fix
added the importorskip to a specific test.
upgrading pytest.
finally figured out importorskip - thanks to @embray
disabling build_sphinx test`
Merge pull request #49 from wkerzendorf/fix_travis_build

Fixing Travis failings - finally all tests skip or pass.