adding R installation to travis
adding R installation to travis

dvingo/atom-beautify,Glavin001/atom-beautify,prettydiff/atom-beautify,prettydiff/atom-beautify,prettydiff/atom-beautify,prettydiff/atom-beautify,Glavin001/atom-beautify,dvingo/atom-beautify,dvingo/atom-beautify,dvingo/atom-beautify,Glavin001/atom-beautify,Glavin001/atom-beautify,Glavin001/atom-beautify,dvingo/atom-beautify