Uncaught TypeError: $.getJSON(...).error is not a function

Hello, I encountered two errors when opening any notebook, how to fix this?
```
Loading extension: snippets/main
main.js?v=20190710093604:42 Uncaught TypeError: $.getJSON(...).error is not a function
at Object.load_extension [as load_ipython_extension] (main.js?v=20190710093604:42)
at utils.js:39
at Object.execCb (require.js?v=951f856e81496aaeec2e71a1c2c0d51f:1693)
at Module.check (require.js?v=951f856e81496aaeec2e71a1c2c0d51f:881)
at Module. (require.js?v=951f856e81496aaeec2e71a1c2c0d51f:1136)
at require.js?v=951f856e81496aaeec2e71a1c2c0d51f:134
at require.js?v=951f856e81496aaeec2e71a1c2c0d51f:1186
at each (require.js?v=951f856e81496aaeec2e71a1c2c0d51f:59)
at Module.emit (require.js?v=951f856e81496aaeec2e71a1c2c0d51f:1185)
at Module.check (require.js?v=951f856e81496aaeec2e71a1c2c0d51f:936)
utils.js:37 Loading extension: splitcell/splitcell
```

```
Loading extension: cell_filter/cell_filter
cell_filter.js?v=20190710093604:77 Uncaught TypeError: $ is not a function
at Object.load_ipython_extension (cell_filter.js?v=20190710093604:77)
at utils.js:39
at Object.execCb (require.js?v=951f856e81496aaeec2e71a1c2c0d51f:1693)
at Module.check (require.js?v=951f856e81496aaeec2e71a1c2c0d51f:881)
at Module. (require.js?v=951f856e81496aaeec2e71a1c2c0d51f:1136)
at require.js?v=951f856e81496aaeec2e71a1c2c0d51f:134
at require.js?v=951f856e81496aaeec2e71a1c2c0d51f:1186
at each (require.js?v=951f856e81496aaeec2e71a1c2c0d51f:59)
at Module.emit (require.js?v=951f856e81496aaeec2e71a1c2c0d51f:1185)
at Module.check (require.js?v=951f856e81496aaeec2e71a1c2c0d51f:936)
main.js?v=20190710093604:393 [varInspector] Restoring Variable Inspector window
```

The report names main.js, cell_filter.js, and the extension-loading path in utils.js. Reproduce the errors by opening a notebook with snippets/main and cell_filter/cell_filter enabled, then trace both stack traces through the extension loader. Done means both extensions load without the reported TypeErrors.

Written by the indexing model from the issue text.