README.md: Update instructions for Ubuntu
The issue that was in the note doesn't seem to occur anymore in
current version of Ubuntu 14.04 so the note is removed. Also added
libsdl2-gfx-dev package which now exists in current Ubuntu 14.04.
@@ -16,8 +16,7 @@ Ubuntu 13.10 may also be used but it may miss an optional package such as
_libsdl2-ttf-dev_ on Ubuntu 13.10's case which is available in Ubuntu 14.04.
On __Ubuntu 14.04 and above__, type:
-`apt-get install libsdl2{,-mixer,-image,-ttf}-dev`
-_Note: Ubuntu 14.04 currently has broken header file in the SDL2 package that disables people from compiling against it. It will be needed to either patch the header file or install SDL2 from source._
+`apt install libsdl2{,-mixer,-image,-ttf,-gfx}-dev`
On __Fedora 20 and above__, type:
`yum install SDL2{,_mixer,_image,_ttf}-devel`
