[retro-gtk] readme: Rename GTK+ into GTK

[Adrien Plazas <aplazas src gnome org>]

commit ae83b91927cc20c43d335799413d560ddf76406c
Author: Adrien Plazas <kekun plazas laposte net>
Date:   Sat Nov 14 19:52:04 2020 +0100

    readme: Rename GTK+ into GTK

 README.md | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)
---
diff --git a/README.md b/README.md
index fad753f7..b61cb3c4 100644
--- a/README.md
+++ b/README.md
@@ -1,13 +1,13 @@
 # RetroGTK
 
-The GTK+ Libretro frontend framework.
+The GTK Libretro frontend framework.
 
 [Libretro](https://www.libretro.com/) is a plugin format design to implement
 video game console emulators, video games and similar multimedia software. Such
 plugins are called Libretro cores.
 
 RetroGTK is a framework easing the usage of Libretro cores in conjunction with
-[GTK+](https://www.gtk.org/).
+[GTK](https://www.gtk.org/).
 
 It encourages the cores to be installed in a well defined centralized place —
 namely the `libretro` subdirectory of your `lib` directory — and it recommends