Setting environment variables change.

The devtools install_github command no longer supports the "args"
parameter. The same effect is achieved by setting the "configure.vars"
parameter.

README.md

@@ -12,7 +12,7 @@ devtools::install_github("SimpleITK/SimpleITKRInstaller")
 or, turn on mutlicore compilation using
 
 ```R
-devtools::install_github("SimpleITK/SimpleITKRInstaller", args=c("--configure-vars=MAKEJ=6"))
+devtools::install_github("SimpleITK/SimpleITKRInstaller", configure.vars=c("MAKEJ=6"))
 ```
 
 Requires _cmake_ and _git_ in the path.