Improve formatting of module docstring

[timholy]

The second extended demo printed in ?VideoIO rendered oddly due to an extra backtick. Save the backticks!

Here's what the end of that docstring looked like previously (the first is fine, the second not):

Here's a brief demo reading through each frame of a video:

  using VideoIO
  r = openvideo(filename)
  img = read(r)
  while !eof(r)
      read!(r, img)
  end

  An example of encoding one frame at a time:

  julia using VideoIO framestack = map(x->rand(UInt8, 100, 100), 1:100) #vector of 2D arrays encoder_options = (crf=23, preset="medium") open_video_out("video.mp4", framestack[1], framerate=24,
  encoder_options=encoder_options) do writer for frame in framestack write(writer, frame) end end`

[codecov[bot]]

Codecov Report

Merging #335 (e4be657) into master (bda9d46) will decrease coverage by 0.20%. The diff coverage is n/a.

@@            Coverage Diff             @@
##           master     #335      +/-   ##
==========================================
- Coverage   81.60%   81.39%   -0.21%     
==========================================
  Files          17       17              
  Lines        1185     1247      +62     
==========================================
+ Hits          967     1015      +48     
- Misses        218      232      +14     

Impacted Files	Coverage Δ
src/VideoIO.jl	54.34% <ø> (ø)
src/util.jl	90.00% <0.00%> (-4.74%)	:arrow_down:
src/testvideos.jl	73.80% <0.00%> (-3.12%)	:arrow_down:
src/avframe_transfer.jl	81.22% <0.00%> (-2.20%)	:arrow_down:
src/avdictionary.jl	8.82% <0.00%> (-0.56%)	:arrow_down:
src/info.jl	100.00% <0.00%> (ø)
src/frame_graph.jl	99.23% <0.00%> (+0.05%)	:arrow_up:
src/encoding.jl	93.33% <0.00%> (+0.09%)	:arrow_up:
src/avio.jl	82.26% <0.00%> (+0.54%)	:arrow_up:
src/avptr.jl	68.88% <0.00%> (+2.22%)	:arrow_up:

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[timholy]

As mentioned in #330, this also fixes CI by changing the version threshold on some broken tests.