BLD: update scikit-bio dependency to >= 0.2.2, < 0.3.0

With scikit-bio 0.2.2, deprecation warnings are reported via `DeprecationWarning`. These are silenced by default in Python 2.7+, so this should hide the warnings from QIIME users. They will still show up in QIIME's unit tests.
Merge pull request #1747 from jairideout/skbio-0.2.2-update

BLD: update scikit-bio dependency to >= 0.2.2, < 0.3.0