pin cython to the version we've been using now that 0.24 is out. [skip ci]

appveyor.yml

@@ -124,7 +124,7 @@ install:
   # pip will build them from source using the MSVC compiler matching the
   # target Python version and architecture
   # NOTE: psutil won't install under PyPy.
-  - "%CMD_IN_ENV% pip install -U wheel cython greenlet psutil"
+  - "%CMD_IN_ENV% pip install -U wheel cython==0.23.5 greenlet psutil"
 
   - ps: "if(Test-Path(\"${env:PYTHON}\\bin\")) {ls ${env:PYTHON}\\bin;}"
   - ps: "if(Test-Path(\"${env:PYTHON}\\Scripts\")) {ls ${env:PYTHON}\\Scripts;}"

dev-requirements.txt

 setuptools
-cython>=0.23.4
+cython==0.23.5
 greenlet>=0.4.9
 coverage>=4.0
 cffi

setup.py

@@ -452,7 +452,7 @@ if run_make and os.path.exists("Makefile"):
     # NOTE: This is effectively pointless and serves only for
     # documentation/metadata, because we run 'make' *before* we run
     # setup(), so installing cython happens too late.
-    setup_requires = ['cython >= 0.23.4']
+    setup_requires = ['cython == 0.23.5']
 else:
     setup_requires = []
 

tox.ini

@@ -5,7 +5,7 @@ envlist =
 [testenv]
 deps =
     greenlet
-    cython >= 0.23.4
+    cython == 0.23.5
     coverage >= 4.0
     psutil
     cffi