Fix the build

[menewman]

https://travis-ci.com/CodeSignal/graphqldoc/jobs/188325664

Jest error:

Test suite failed to run
    Jest encountered an unexpected token
    This usually means that you are trying to import a file which Jest cannot parse, e.g. it's not plain JavaScript.
    By default, if Jest sees a Babel config, it will use that to transform your files, ignoring "node_modules".
    Here's what you can do:
     • To have some of your "node_modules" files transformed, you can specify a custom "transformIgnorePatterns" in your config.
     • If you need a custom transformation specify a "transform" option in your config.
     • If you simply want to mock your non-JS modules (e.g. binary assets) you can stub them out with the "moduleNameMapper" config option.
    You'll find more details and examples of these config options in the docs:
    https://jestjs.io/docs/en/configuration.html
    Details:
    SyntaxError: /home/travis/build/CodeSignal/graphqldoc/plugins/__test__/navigation.interface.test.ts: Unexpected token (5:19)
      3 | import NavigationInterfaces from '../navigation.interface';
      4 | 
    > 5 | const introspection: Introspection = require('./empty.schema.json');
        |                    ^
      6 | const projectPackage: any = require('./projectPackage.json');
      7 | 
      8 | describe('pĺugins/navigation.interface#NavigationInterfaces', () => {

I thought I already fixed this with ts-jest, but evidently not.