Updating to newest nupic.core

Testing compatibility of latest nupic.core SHA.

Here are the [nupic.core changes](https://github.com/numenta/nupic.core/compare/86f577e4af49f413bb8c46ca1ada4d673e146573...b9a24e19e97e5109011043d0f3ae2491b14065d8) included in this SHA bump. It consists almost entirely of documentation.