Broken chapter reference

[nirski]

The chapter link reference is not displaying.

spatial-microsim-book/01-introduction.Rmd

Line 230 in cdba7ae

Chapter \ref{smsimr}).

[Robinlovelace]

Thanks @nirski. I have not worked on the book for a while and have limited capacity to update it at present. Any Pull Request to fix it welcome, can you get it working locally? Impressive if so!