TST: Add minter error test
TST: Add minter error test

Verifies that an OperationError is raised when attempting to
access the minter on an MSA created with keys

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