Update dependency ts-jest to v26

[renovate]

This PR contains the following updates:

Package	Type	Update	Change
ts-jest (source)	devDependencies	major	25.5.1 -> 26.0.0

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Release Notes

kulshekhar/ts-jest

v26.0.0

Compare Source

Bug Fixes

• compiler: return undefined for getScriptVersion when a file doesn't exist in memory cache (#​1641) (6851b8e)

Features

• support Jest v26 (#​1602) (23b7741)

BREAKING CHANGES

• Requires a minimum of TypeScript v3.8
• Drop support for Node 8

25.5.1 (2020-05-09)

Bug Fixes

• compiler: don't resolve files from build folder for projectReferences (#​1614) (74b92d3)
• config: don't set include value of tsconfig to empty array (#​1606) (8a29aaa)

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