boilerplate.py: accept 2018
boilerplate.py: accept 2018

Happy New Year! 2018 is now a valid year for the copyright notice in a
file's header.

kubernetes/minikube,dalehamel/minikube,kubernetes/minikube,aaron-prindle/minikube,r2d4/minikube,kubernetes/minikube,r2d4/minikube,dlorenc/minikube,warmchang/minikube,dims/minikube,dlorenc/minikube,warmchang/minikube,dalehamel/minikube,kubernetes/minikube,dims/minikube,dlorenc/minikube,dims/minikube,dlorenc/minikube,aaron-prindle/minikube,dlorenc/minikube,aaron-prindle/minikube,warmchang/minikube,warmchang/minikube,dlorenc/minikube,dalehamel/minikube,kubernetes/minikube,kubernetes/minikube,kubernetes/minikube,dlorenc/minikube,r2d4/minikube,dlorenc/minikube,warmchang/minikube,warmchang/minikube,warmchang/minikube