Update dependency deepmerge to v4

[renovate]

This PR contains the following updates:

Package	Change	Age	Adoption	Passing	Confidence
deepmerge	^2.0.1 -> ^4.0.0

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Release Notes

TehShrike/deepmerge (deepmerge)

v4.3.1

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• Fix type definition for arrayMerge options. #​239

v4.3.0

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• Avoid thrown errors if the target doesn't have propertyIsEnumerable. #​252

v4.2.2

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• isMergeableObject is now only called if there are two values that could be merged. a34dd4d2

v4.2.1

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• Fix: falsey values can now be merged. #​170

v4.2.0

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• Properties are now only overwritten if they exist on the target object and are enumerable. #​164

Technically this could probably be a patch release since "which properties get overwritten" wasn't documented and accidentally overwriting a built-in function or some function up the property chain would almost certainly be undesirable, but it feels like a gray area, so here we are with a feature version bump.

v4.1.2

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• Rolled back #​167 since Object.assign breaks ES5 support. 55067352

v4.1.1

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• The options argument is no longer mutated #​167

v4.1.0

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• cloneUnlessOtherwiseSpecified is now exposed to the arrayMerge function #​165

v4.0.0

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• The main entry point in package.json is now a CommonJS module instead of a UMD module #​155

v3.3.0

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• Enumerable Symbol properties are now copied #​151

v3.2.1

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• bumping dev dependency versions to try to shut up bogus security warnings from Github/npm #​149

v3.2.0

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• feature: added the customMerge option #​133

v3.1.0

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• typescript typing: make the all function generic #​129

v3.0.0

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• drop ES module build #​123

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