contrib: srt: update to 1.5.3
Tested with:
# push a stream
gst-launch-1.0 -v videotestsrc ! video/x-raw, height=360, width=640 ! videoconvert ! x264enc tune=zerolatency ! video/x-h264, profile=high ! mpegtsmux ! srtsink uri=srt://:8888
# read the stream
./vlc srt://127.0.0.1:8888