Add SameSite in Cookie struct 
Add SameSite in Cookie struct 

Go source code v1.15 contains SameSite: https://golang.org/src/net/http/cookie.go

Also remove unnecessary code source indentation.
astaxie/build-web-application-with-golang,astaxie/build-web-application-with-golang,astaxie/build-web-application-with-golang