Fixed Makefile.

Signed-off-by: Kouhei Maeda <mkouhei@palmtb.net>
Fixed golint violations.

Signed-off-by: Kouhei Maeda <mkouhei@palmtb.net>
Fixed go vet error.

Signed-off-by: Kouhei Maeda <mkouhei@palmtb.net>