`go build` wants to add the current go version to go.mod as the
minimum every time we run `make` in the directory. Add 1.11 (the
earliest Go version that supports modules) there to make it happy.
Signed-off-by: George Dunlap <george.dunlap@citrix.com> Reviewed-by: Nick Rosbrook <rosbrookn@ainfosec.com>