grpc: go generate (#2712)

*grpc* was added manually; do a go generate to add it, so we don't have
future diffs.

Signed-off-by: Miek Gieben <miek@miek.nl>

core/dnsserver/zdirectives.go

@@ -44,8 +44,8 @@ var Directives = []string{
 	"loop",
 	"forward",
 	"proxy",
+	"grpc",
 	"erratic",
 	"whoami",
 	"on",
-	"grpc",
 }