Update minor devDeps

[renovate]

This PR contains the following updates:

Package	Type	Update	Change
jest (source)	devDependencies	patch	25.5.2 -> 25.5.4
jest-cli (source)	devDependencies	patch	25.5.2 -> 25.5.4
postcss (source)	devDependencies	patch	7.0.27 -> 7.0.28
react-hot-loader	devDependencies	patch	4.12.20 -> 4.12.21

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Release Notes

facebook/jest

v25.5.4

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Fixes

• [jest-jasmine2] Don't run beforeAll / afterAll in skipped describe blocks (#​9931)

Chore & Maintenance

• [jest-runtime] Do not warn when mutating require.cache (#​9946)

v25.5.3

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Chore & Maintenance

• [jest-circus] Fix memory leak when running in band (#​9934)

postcss/postcss

v7.0.28

Compare Source

• Fix TypeScript definition (by Natalie Weizenbaum).

gaearon/react-hot-loader

v4.12.21

Compare Source

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