depends: change xlib dependencies

The latest upstream git master requires libXv.so, libX11.so and
libXext.so for enabling xlib. Although this requirement is
currently present only on git master, by examining the changes
it seems to make sense to add it here too.

References
----------
http://git.videolan.org/?p=ffmpeg.git;a=commit;h=0736f32a4facddbd953977ca614a3ee6d8a6e1d7

PKGBUILD

@@ -4,7 +4,7 @@
 pkgname=ffmpeg-full
 _srcname=ffmpeg
 pkgver=4.0
-pkgrel=2
+pkgrel=3
 pkgdesc='Complete solution to record, convert and stream audio and video (all possible features including nvenc, qsv and libfdk-aac)'
 arch=('i686' 'x86_64')
 url='http://www.ffmpeg.org/'
@@ -20,7 +20,8 @@ depends=(
         'libssh' 'tesseract' 'libtheora' 'twolame' 'v4l-utils' 'vid.stab' 'libvorbis'
         'libvpx' 'wavpack' 'libwebp' 'libx264.so' 'x265' 'libxcb' 'xvidcore' 'libxml2'
         'zimg' 'zeromq' 'zvbi' 'lilv' 'xz' 'openal' 'opencl-icd-loader' 'mesa' 'sndio'
-        'sdl2' 'libx11' 'zlib' 'libomxil-bellagio' 'libva' 'libdrm' 'libvdpau'
+        'sdl2' 'libxv' 'libx11' 'libxext' 'zlib' 'libomxil-bellagio' 'libva' 'libdrm'
+        'libvdpau'
     # AUR:
         'chromaprint-fftw' 'aom-git' 'codec2' 'flite1-patched' 'libilbc' 'kvazaar'
         'openh264' 'libopenmpt-svn' 'shine' 'vo-amrwbenc' 'xavs' 'ndi-sdk' 'libmysofa'