Fix RGB to HSL conversion

[JimBobSquarePants]

Prerequisites

• I have written a descriptive pull-request title
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• I have provided test coverage for my change (where applicable)

Description

Fixes the calculation issue discovered in #997

[codecov]

Codecov Report

❗ No coverage uploaded for pull request base (master@29d7ed0). Click here to learn what that means.
The diff coverage is 100%.

@@            Coverage Diff            @@
##             master    #1001   +/-   ##
=========================================
  Coverage          ?   89.77%           
=========================================
  Files             ?     1098           
  Lines             ?    48812           
  Branches          ?     3433           
=========================================
  Hits              ?    43823           
  Misses            ?     4284           
  Partials          ?      705

Impacted Files	Coverage Δ
.../Colorspaces/Conversion/RgbAndHslConversionTest.cs	100% <ø> (ø)
...on/Implementation/Converters/HslAndRgbConverter.cs	98.24% <100%> (ø)

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Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
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[codecov]

Codecov Report

❗ No coverage uploaded for pull request base (master@29d7ed0). Click here to learn what that means.
The diff coverage is 100%.

@@            Coverage Diff            @@
##             master    #1001   +/-   ##
=========================================
  Coverage          ?   89.66%           
=========================================
  Files             ?     1098           
  Lines             ?    48810           
  Branches          ?     3433           
=========================================
  Hits              ?    43766           
  Misses            ?     4289           
  Partials          ?      755

Impacted Files	Coverage Δ
.../Colorspaces/Conversion/RgbAndHslConversionTest.cs	100% <ø> (ø)
...on/Implementation/Converters/HslAndRgbConverter.cs	98.24% <100%> (ø)

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 29d7ed0...7aaaa25. Read the comment docs.