put dependencies in the right place

Author: alimanfoo

tox.ini

@@ -10,14 +10,14 @@ envlist = py27, py34, py35, py36, docs
 setenv =
     PYTHONHASHSEED = 42
 commands =
-    py27: pip install -U backports.lzma
     python setup.py build_ext --inplace
     py27,py34,py35: nosetests -v numcodecs --with-coverage --cover-erase --cover-package=numcodecs
     py36: nosetests -v --with-coverage --cover-erase --cover-package=numcodecs --with-doctest --doctest-options=+NORMALIZE_WHITESPACE numcodecs
     py36: flake8 --max-line-length=100 numcodecs
     python setup.py bdist_wheel
     coverage report -m
 deps =
+    py27: backports.lzma
     -rrequirements_dev.txt
 
 [testenv:docs]