webpack/babel: Properly transpile spread operator in react-leaflet (#3178)
webpack/babel: Properly transpile spread operator in react-leaflet (#3178)

react-leaflet currently does not work on Microsoft Edge 18 (and possibly
Mobile Safari 11.2). A fix was attempted in commit 8e7d591af825e53b1cb199a9b59458264c4fc1a3.

However, the fix was incomplete for a few reasons:
1. The stated path did not reference the correct directory for
   react-leaflet.
2. There are 2 react-leaflet directories (react-leaflet and
   @react-leaflet) which use the spread operator.

Properly fix the issue by including the full path to both directories.

Note:
An alternate fix is to use regex again (e.g. /../node_modules\/react-leaflet/).
However, I used absolute paths according to the best practices stated in [1].

[1]: https://webpack.js.org/configuration/#:~:text=//%20-%20Use%20arrays%20of%20absolute%20paths%20in%20include%20and%20exclude%20to%20match%20the%20full%20path

Fixes #3147
nusmodifications/nusmods,nusmodifications/nusmods,nusmodifications/nusmods,nusmodifications/nusmods