plyr error

[jkylearmstrong]

I get the following error:

## You have loaded plyr after dplyr - this is likely to cause problems.
## If you need functions from both plyr and dplyr, please load plyr first, then dplyr:
## library(plyr); library(dplyr)

This is because in the package there is an explicate library call:

library(plyr)

inside of https://github.com/vqv/ggbiplot/blob/master/R/ggbiplot.r

inside of packages the RoxyGen @importFrom tag

dplyr is in direct conflict with plyr

[wesley4546]

I created a pull request to fix this #69