docs(readme): update readme with @next info
docs(readme): update readme with @next info

Signed-off-by: Will Soto <e88b744add47cc3da30186f5601865928acd804d@gmail.com>

willsoto/angular-chartist.js,paradox41/angular-chartist.js,willsoto/angular-chartist.js,paradox41/angular-chartist.js