doc/APIChanges: fix lavu version numbers in a few recent entries

Signed-off-by: James Almer <jamrial@gmail.com>

doc/APIchanges

@@ -103,14 +103,14 @@ API changes, most recent first:
 2017-11-xx - xxxxxxx - lavc 58.4.100 - avcodec.h
   Add AVCodecHWConfig and avcodec_get_hw_config().
 
-2017-11-22 - 3650cb2dfa - lavu 55.3.100 - opencl.h
+2017-11-22 - 3650cb2dfa - lavu 56.3.100 - opencl.h
   Remove experimental OpenCL API (av_opencl_*).
 
-2017-11-22 - b25d8ef0a7 - lavu 55.2.100 - hwcontext.h hwcontext_opencl.h
+2017-11-22 - b25d8ef0a7 - lavu 56.2.100 - hwcontext.h hwcontext_opencl.h
   Add AV_HWDEVICE_TYPE_OPENCL and a new installed header with
   OpenCL-specific hwcontext definitions.
 
-2017-11-22 - a050f56c09 - lavu 55.1.100 - pixfmt.h
+2017-11-22 - a050f56c09 - lavu 56.1.100 - pixfmt.h
   Add AV_PIX_FMT_OPENCL.
 
 2017-11-11 - 48e4eda11d - lavc 58.3.100 - avcodec.h