Minor readme typo. "commmon" -> "common"

[Jaben]

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Description

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Codecov Report

❗ No coverage uploaded for pull request base (master@5e2a7cb). Click here to learn what that means.
The diff coverage is n/a.

@@            Coverage Diff            @@
##             master    #1200   +/-   ##
=========================================
  Coverage          ?   82.58%           
=========================================
  Files             ?      694           
  Lines             ?    30047           
  Branches          ?     3397           
=========================================
  Hits              ?    24814           
  Misses            ?     4535           
  Partials          ?      698           

Flag	Coverage Δ
#unittests	82.58% <ø> (?)

Impacted Files	Coverage Δ
...Sharp/Processing/IImageProcessingContextFactory.cs	100.00% <0.00%> (ø)
...s/Conversion/Implementation/LmsAdaptationMatrix.cs	100.00% <0.00%> (ø)
...harp/Memory/Allocators/ArrayPoolMemoryAllocator.cs	96.61% <0.00%> (ø)
...lorSpaces/Conversion/ColorSpaceConverterOptions.cs	57.14% <0.00%> (ø)
...TagDataEntries/IccViewingConditionsTagDataEntry.cs	52.00% <0.00%> (ø)
...Processors/Transforms/Resamplers/WelchResampler.cs	100.00% <0.00%> (ø)
src/ImageSharp/ImageFrameCollection.cs	90.00% <0.00%> (ø)
...cessing/Extensions/Filters/BlackWhiteExtensions.cs	100.00% <0.00%> (ø)
.../Formats/Jpeg/Components/Decoder/JpegFileMarker.cs	100.00% <0.00%> (ø)
...ssing/Processors/Dithering/OrderedDitherFactory.cs	100.00% <0.00%> (ø)
... and 684 more

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[JimBobSquarePants]

Thanks @Jaben If you can please sign the Contributor License Agreement we can get this merged 👍