bump greenlet

dev-requirements.txt

 setuptools
 wheel
 cython>=0.24
-greenlet>=0.4.9
+greenlet>=0.4.10
 prospector[with_pyroma]
 coverage>=4.0
 coveralls>=1.0

setup.py

@@ -81,7 +81,7 @@ if PYPY:
     # have some serious crashing bugs with GC interacting with cython,
     # so this is disabled
 else:
-    install_requires = ['greenlet >= 0.4.9']
+    install_requires = ['greenlet >= 0.4.10'] # TODO: Replace this with platform markers?
     setup_requires = []