TST: use six.assertRaisesRegex instead of deprecated assertRaisesRegexp
TST: use six.assertRaisesRegex instead of deprecated assertRaisesRegexp

gregcaporaso/scikit-bio,kdmurray91/scikit-bio,anderspitman/scikit-bio,kdmurray91/scikit-bio,gregcaporaso/scikit-bio,anderspitman/scikit-bio