Update dependency pixelmatch to v5

[renovate-bot]

This PR contains the following updates:

Package	Type	Update	Change
pixelmatch	devDependencies	major	4.0.2 -> 5.1.0

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Release Notes

mapbox/pixelmatch

v5.1.0

Compare Source

Added diffMask option. #​73 (h/t @​tmeasday)

v5.0.2

Compare Source

• Fix input validation failing in some Jest environments. #​62

v5.0.1

Compare Source

• 🐞 Fix alpha option being ignored in case of identical images.
• Slightly more robust input validation.

v5.0.0

Compare Source

• ⚠️ 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.

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