Bump simpervisor version

Fixes #227

Brings in jupyterhub/simpervisor#7

Author: yuvipanda

setup.py

@@ -15,7 +15,7 @@
     long_description=readme,
     long_description_content_type="text/markdown",
     packages=setuptools.find_packages(),
-    install_requires=['notebook', 'simpervisor>=0.2', 'aiohttp'],
+    install_requires=['notebook', 'simpervisor>=0.4', 'aiohttp'],
     python_requires='>=3.5',
     classifiers=[
         'Framework :: Jupyter',