Corrects documentation error

Item 22. in cdist description had parenthetical that read "see sokalsneath function documentation", but should have read, "see wminkowski function documentation." That is fixed here.
Merge pull request #3012 from lemonlaug/master

DOC: corrects documentation error in spatial.cdist
MAINT: Remove duplicated words in docstrings or comments in python files (plus a little copy-editing afterwards).
MAINT: Remove a few duplicated words in the docs.
Merge pull request #3016 from WarrenWeckesser/remove-dup-words

Remove duplicated words in documentation or comments.
MAINT: stats: remove unused import from contingency.py
MAINT: stats: remove a couple unused variables in mstats_basic.py
MAINT: stats: remove a couple unused variables in vonmises.py
Merge pull request #3017 from WarrenWeckesser/stats-maint

A bit of maintenance work in stats.
.travis.yml: pip install from wheels to avoid lengthy compilations
MAINT: remove unnecessary things from .travis.yml
Merge pull request #3020 from  msabramo/travis_use_wheels

MAINT: .travis.yml: pip install from wheels to avoid lengthy compilations
MAINT: runtests: add option for gcov
Merge pull request #3021 from pv/gcov

MAINT: runtests: add option for gcov
DOC: logit and expit docstrings -- fix typo and add versionadded
DOC: typo contrained->constrained
DOC: versionadded for some special functions
Merge pull request #3027 from argriffing/typo-contrained

DOC: typo contrained->constrained
Merge pull request #3028 from argriffing/versionadded-xlogy

DOC: versionadded for some special functions
GEN: special: regenerate _ufuncs.pyx