getImageCacheKey = ({ fluid, fixed }) => {
  const srcData = getCurrentSrcData(fluid || fixed || [])

  return srcData && srcData.src
}
Find the source of an image to use as a key in the image cache.
Use `the first image in either `fixed` or `fluid`
@param {{fluid: {src: string, media?: string}[], fixed: {src: string, media?: string}[]}} args
@return {string?} Returns image src or undefined it not given.