message: ffmpeg: update wrapper
  FFmpeg: 3.3.4 -> 3.4.2
  LibVPX: 1.6.1 -> 1.7.0
  OpenH264: 1.6.0 -> 1.7.0
diff: -# Binary branch name: ffmpeg/master_20171009
  -# Binaries were created for OpenCV: 8ac2c5d620b467d3f22802e96c88ddde6da707af
  -set(FFMPEG_BINARIES_COMMIT "66b1fed06cf3510235f367f96aa26da5cb234a15")
  -set(FFMPEG_FILE_HASH_BIN32 "3ae76b105113d944984b2351c61e21c6")
  -set(FFMPEG_FILE_HASH_BIN64 "cf3bb5bc9d393b022ea7a42eb63e794d")
  -set(FFMPEG_FILE_HASH_CMAKE "ec59008da403fb18ab3c1ed66aed583b")
  +# Binaries branch name: ffmpeg/master_20180220
  +# Binaries were created for OpenCV: 9819ebc0954c2df62943ebbd5936d325e5dc89e1
  +ocv_update(FFMPEG_BINARIES_COMMIT "0a0e88972a7ea97708378d0488a65f83e7cc5e69")
  +ocv_update(FFMPEG_FILE_HASH_BIN32 "b8120c07962d591e2e9071a1bf566fd0")
  +ocv_update(FFMPEG_FILE_HASH_BIN64 "dc9c50e7b05482acc25d6ce0ac61bf1d")
  +ocv_update(FFMPEG_FILE_HASH_CMAKE "3b90f67f4b429e77d3da36698cef700c")
  function(download_win_ffmpeg script_var)
  set(${script_var} "" PARENT_SCOPE)
  