BLD: fix failing vbench cases
BLD: travis changes forced system site-packages now unavailable
BLD: fix nose version at 1.3.0 to avoid py3 issues
DOC: add notes to the groupby.rst docs
Fix for GH 6885 - get_dummies chokes on unicode values
Merge pull request #7008 from immerrr/fix-failing-vb-suites

BLD: fix failing vbench cases