Bug/Compatibility 1.0.22: Arrows Function breaks IE11

[f-aubert]

Hello, in upgrading I found out that a newly added arrow function breaks compatibility with IE. Could it be avoided?

Here: const transformFn = encoding === 'hsl' ? c => c // If HSL return as incame : colorsys.getTransformEncodingFunction(nextHsl, encoding)

if (typeof transformFn !== 'function') { return color }

[jsdario]

Sure, could you submit a quick PR?

Sorry for taking so long to answer.