lock development requirements, at least for travis

to avoid changes in the testing tools causing issues for our oldstable
version, lock stuff to a proven version.

.travis/install.sh

@@ -45,7 +45,7 @@ fi
 
 python -m virtualenv ~/.venv
 source ~/.venv/bin/activate
-pip install -r requirements.d/development.txt
+pip install -r requirements.d/development.lock.txt
 pip install codecov
 python setup.py --version
 pip install -e .[fuse]

requirements.d/development.lock.txt

@@ -0,0 +1,9 @@
+virtualenv==13.1.2
+setuptools-scm==3.1.0
+pluggy==0.6.0
+tox==3.1.3
+pytest==3.5.1
+pytest-xdist==1.24.0
+pytest-cov==2.6.0
+pytest-benchmark==3.1.1
+Cython==0.29