Change shinyFilters Install Instructions

[dantetrick]

Hello Dave,

Thank you for the great package. Appreciate your work.

I was re-installing the package using the instructions in the GIT repo and noticed that the current method doesn't work anymore.
devtools::install_github("davesteps/shinyFilters")

I was able to successfully install and load using the following method.
devtools::install_git("https://github.com/davesteps/shinyFilters.git")