add pacman as a import

[carlislerainey]

When installing the GitHub version, I get a missing package error for pacman. (There might be others as well that I happen to already have installed.)

See the error below.

> # install package
> library(devtools)
> install_github("soodoku/ethnicolor")

Downloading GitHub repo soodoku/ethnicolor@master
from URL https://api.github.com/repos/soodoku/ethnicolor/zipball/master
Installing ethnicolor
'/Library/Frameworks/R.framework/Resources/bin/R' --no-site-file --no-environ --no-save --no-restore --quiet CMD  \
  INSTALL  \
  '/private/var/folders/zq/3_bjyh6d0tbgkgr7sltfj3r00000gq/T/Rtmp5zPxC3/devtools44a32d1d7234/appeler-ethnicolor-054b7fa'  \
  --library='/Library/Frameworks/R.framework/Versions/3.4/Resources/library' --install-tests 

* installing *source* package ‘ethnicolor’ ...
** R
** inst
** tests
** preparing package for lazy loading
Error in library(pacman) : there is no package called ‘pacman’
Error : unable to load R code in package ‘ethnicolor’
ERROR: lazy loading failed for package ‘ethnicolor’
* removing ‘/Library/Frameworks/R.framework/Versions/3.4/Resources/library/ethnicolor’
Installation failed: Command failed (1)

I suggest adding it as an import so that it is automatically installed. http://r-pkgs.had.co.nz/description.html#dependencies