Update Cython Magics.ipynb

Restore name and signature.

examples/Builtin Extensions/Cython Magics.ipynb

@@ -1,7 +1,7 b''
 {
  "metadata": {
-  "name": "",
-  "signature": "sha256:91a890584d01fd61b1b252f257244d3facd2c1cc9d021d83dc894b97d9a0c47d"
+  "name": "Cython Magics",
+  "signature": "sha256:c357b93e9480d6347c6677862bf43750745cef4b30129c5bc53cb879a19d4074"
  },
  "nbformat": 3,
  "nbformat_minor": 0,
@@ -363,4 +363,4 b''
    "metadata": {}
   }
  ]
-}
  No newline at end of file
+}