Merge pull request #70 from springermac/pyup-pin-pytest-3.2.1

Pin pytest to latest version 3.2.1

tests/requirements-tools.txt

@@ -2,7 +2,7 @@
 git+https://github.com/pytest-dev/execnet.git
 
 # For running tests
-pytest  # pyup: >=2.7.3 # Testing framework.
+pytest==3.2.1  # pyup: >=2.7.3 # Testing framework.
 pytest-xdist==1.19.1     # Plugin allowing running tests in parallel.
 pytest-timeout==1.2.0   # Plugin to abort hanging tests.
 pytest-catchlog==1.2.2  # Capture log output separately from stdout/stderr