examples: correct typo in keepalive example (#2645)
examples: correct typo in keepalive example (#2645)


thinkerou/grpc-go,stanley-cheung/grpc-go,stanley-cheung/grpc-go,dfawley/grpc-go,dfawley/grpc-go,menghanl/grpc-go,grpc/grpc-go,menghanl/grpc-go,thinkerou/grpc-go,grpc/grpc-go