added install requirement for cython

Author: jimy-byerley

.travis.yml

@@ -23,7 +23,7 @@ jobs:
         - ln -s /c/Python39/python.exe /c/Python39/python3.exe
 
 install:
-  - python3 -m pip install cibuildwheel==1.11.1.post1
+  - python3 -m pip install cibuildwheel==1.11.1.post1 cython>=0.29
 
 script:
   # build the wheels, put them into './wheelhouse'