gnome-screenshot does not allow to set delay when taking screenshot of area (gnome-screenshot --area --delay N)

[Norbert]

Steps to reproduce:
1. Try to make delayed screenshot of area with `gnome-screenshot --area --delay 10`

Expected results:
User is able to set delay when taking screenshot of area

Actual results:
User is unable to set delay when taking screenshot of area because of options conflict (but why?):

```
$ gnome-screenshot --area --delay 10
Conflicting options: --area and --delay should not be used at the same time.
```

First seen on AskUbuntu (https://askubuntu.com/q/1008771/66509).

ProblemType: Bug
DistroRelease: Ubuntu 17.10
Package: gnome-screenshot 3.25.0-0ubuntu2
ProcVersionSignature: Ubuntu 4.13.0-32.35-generic 4.13.13
Uname: Linux 4.13.0-32-generic x86_64
ApportVersion: 2.20.7-0ubuntu3.7
Architecture: amd64
CurrentDesktop: ubuntu:GNOME
Date: Fri Feb 23 01:42:37 2018
ProcEnviron:
 TERM=xterm-256color
 PATH=(custom, no user)
 XDG_RUNTIME_DIR=<set>
 LANG=en_US.UTF-8
 SHELL=/bin/bash
SourcePackage: gnome-screenshot
UpgradeStatus: No upgrade log present (probably fresh install)

[Sebastien Bacher (seb128)]

The option is available in git now

https://gitlab.gnome.org/GNOME/gnome-screenshot/-/commit/164e779a