'could not find path to 'gnuplot' error in go-gnuplot

On Debina, the code is written in Golang (version 1.6.2).
I'd like to use the library in github.com.
There is an error and I am troubled because I do not know how to correct it.
I'm asking you a question because I want someone to teach me.

I would like to install a library called go-gnuplot.

go get github.com/sbinet/go-gnuplot

I was able to confirm that this library was installed in
github.com/sbinet/go-gnuplot. Therefore, copy the sample code described in url above (assuming test.gognuplot.go) and

go run test.gognuplot.go

When I started it in , I got the following error:

** could not find path to 'gnuplot':
exec: "gnuplot" —executable file not found in $PATH
panic —Could not find 'gnuplot'

goroutine1 [running]:
panic (0x4dc060, 0xc82000a330)
        /home/xxx/.gvm/gos/go1.6.2/src/runtime/panic.go:481+0x3e6
github.com/sbinet/go-gnuplot.init.1()
        /home/xxx/.gvm/pkgsets/go1.6.2/global/src/github.com/sbinet/go-gnuplot/gnuplot.go:32+0x1aa
github.com/sbinet/go-gnuplot.init()
        /home/xxx/.gvm/pkgsets/go1.6.2/global/src/github.com/sbinet/go-gnuplot/gnuplot.go:446+0x54
main.init()
        /home/xxx/programs/go/test.gognuplot.go:26+0x3b
exit status2

I thought it was $PATH, so I looked at echo$PATH and found
/home/xxx/bin:/home/xxx/.gvm/pkgsets/go1.6.2/global/bin:/home/xxx/.gvm/gos/go1.6.2/bin:/home/xxx/.gvm/pkgsets/go1.6.2/global/overlay/bin:/home/xxx/.gvm/bin/bin:/local/bin:/bin:/home/bin/bin/bin/home/bin/bin/bin/bin/home/bin/bin: That was it.

By the way, $GOPATH is
/home/xxx/.gvm/pkgsets/go1.6.2/global
That's it.

I think the error is that PATH is not passing.
Without this library, there is no bin, so I don't know where to fix it.

I am troubled because I don't know how to correct the error.
May I speak to you?Thank you for your cooperation.