With following example:
```
#+begin_src gnuplot :session :results graphics :file "data/images/sin.png"
:cache no
set term png
set grid
plot sin(x), cos(x)
#+end_src
```
If I use Org-mode ELPA version. then it works fine.
But when I use `master` branch version, then it does not have any result.
Tried to check out git log of recently commits, and `ob-core.el` file
recent git log commits, and `ob-gnuplot.el`'s. But does not found any
suspicious commits yet.

Environment info:
- Arch Linux
- Emacs version: GNU Emacs 27.0.50 (build 1, x86_64-pc-linux-gnu, GTK+
Version 3.22.26) of 2018-02-10
- Org-mode version: Org mode version 9.1.7 (9.1.7-elpaplus @ mixed
installation! /home/stardiviner/.emacs.d/elpa/org-plus-contrib-20180226/
and /home/stardiviner/Code/Emacs/org-mode/lisp/)

[stardiviner]           <Hack this world!>      GPG key ID: 47C32433
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Blog: http://stardiviner.github.io/