Update dependency ts-jest to v26.4.2

[renovate[bot]]

This PR contains the following updates:

Package	Type	Update	Change
ts-jest (source)	devDependencies	patch	26.4.1 -> 26.4.2

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Release Notes

kulshekhar/ts-jest

### [`v26.4.2`](https://togithub.com/kulshekhar/ts-jest/blob/master/CHANGELOG.md#​2642-httpsgithubcomkulshekharts-jestcomparev2641v2642-2020-10-23) [Compare Source](https://togithub.com/kulshekhar/ts-jest/compare/v26.4.1...v26.4.2) ##### Features - **config:** expose several typings as public apis ([#​2054](https://togithub.com/kulshekhar/ts-jest/issues/2054)) ([3b6b705](https://togithub.com/kulshekhar/ts-jest/commit/3b6b7055e2b9c74e81fb91596c807ace02ab77a1)) ##### Performance Improvements - **compiler:** speed up bootstrap time for `isolatedModules:false` ([#​2055](https://togithub.com/kulshekhar/ts-jest/issues/2055)) ([230b5dd](https://togithub.com/kulshekhar/ts-jest/commit/230b5ddbee55357d25dd190cd45aa8a30d7f31e0)) ##### DEPRECATIONS - **config**: deprecate `tsConfig` in favor of `tsconfig` ([#​1997](https://togithub.com/kulshekhar/ts-jest/pull/1997)) - **config**: deprecate `packageJson` since internal codes don't use it anymore ([#​2034](https://togithub.com/kulshekhar/ts-jest/pull/2034))

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