Give more specific error message if Shiny isn't found on the system.
Give more specific error message if Shiny isn't found on the system.

joequant/shiny-server,sneumann/shiny-server,dpryan79/shiny-server,joequant/shiny-server,ekergy/shiny-ekergy,nvoron23/shiny-server,trestletech/shiny-server,ekergy/shiny-ekergy,dpryan79/shiny-server,trestletech/shiny-server,sneumann/shiny-server,dpryan79/shiny-server,nvoron23/shiny-server,githubfun/shiny-server,sneumann/shiny-server,trestletech/shiny-server,ekergy/shiny-ekergy,joequant/shiny-server,githubfun/shiny-server,sneumann/shiny-server,nvoron23/shiny-server,githubfun/shiny-server,sneumann/shiny-server,ekergy/shiny-ekergy,githubfun/shiny-server,trestletech/shiny-server,githubfun/shiny-server,trestletech/shiny-server,dpryan79/shiny-server,sneumann/shiny-server,githubfun/shiny-server,joequant/shiny-server,trestletech/shiny-server,joequant/shiny-server,dpryan79/shiny-server,nvoron23/shiny-server,ekergy/shiny-ekergy,nvoron23/shiny-server,ekergy/shiny-ekergy,sneumann/shiny-server,githubfun/shiny-server,dpryan79/shiny-server,joequant/shiny-server,dpryan79/shiny-server,ekergy/shiny-ekergy,nvoron23/shiny-server,joequant/shiny-server