v5.0.0

• ⚠️ Breaking: update to ES6 syntax, dropping Node <6.4 and IE11 support.
• 🎨 Added configurable diff output (options alpha, aaColor, diffColor) (@dreignier @VP-)
• ⚡️ Improve matching performance by ~35%.
• ⚡️ Bypass detailed comparison when image data is identical, significantly improving performance when running tests on CI #60 (thanks to @bontscho).
• Fix anti-aliasing detection on image edges #51 (@IvanSanchez).
• Produce a meaningful error when image data is in the wrong format #53 (thanks to @LearningNerd)
• CLI: return non-zero exit code when images differ #54 (@maio).
• CLI: make diff output optional.
• Make the published NPM module smaller.