huge performance drop when js files are included in the transform property with ts-jest

[LoganTann]

Please see this issue and reproduction : kulshekhar/ts-jest#4294

In the https://github.com/thisismydesign/nestjs-starter/blob/master/jest.config.ts#L8 file :

• the line '^.+\\.(t|j)s$': 'ts-jest',
• should be replaced by '^.+\\.ts$': 'ts-jest',