I got around this by downloading from CRAN the version of httpuv that was active two weeks ago: httpuv_1.3.6.2.tar.gz
I stored it in /home/fjcc/Downloads
I then ran
sudo su - -c "R -e \"install.packages('/home/fjcc/Downloads/httpuv_1.3.6.2.tar.gz', repos = NULL, type = 'source')\""
sudo su - -c "R -e \"install.packages('shiny', repos = 'https://cran.rstudio.com')\""
This succeeded and I can run
library(shiny)
from inside R.
So it seems the latest shiny is not compatible with the latest httpuv, at least on my R 3.3.3 on a Raspbian O/S but going back to httpuv_1.3.6.2 does work.