Fix typo

```
HTTPError: 400 Bad Request from https://upload.pypi.org/legacy/
Invalid value for classifiers. Error: Classifier 'License :: OSI Approved :: MiT License' is not a valid classifier.
```

Author: ryantam626

setup.py

@@ -81,7 +81,7 @@
     platforms="Linux, Mac OS X, Windows",
     keywords=["Jupyter", "JupyterLab", "JupyterLab3"],
     classifiers=[
-        "License :: OSI Approved :: MiT License",
+        "License :: OSI Approved :: MIT License",
         "Programming Language :: Python",
         "Programming Language :: Python :: 3",
         "Programming Language :: Python :: 3.6",