update(ts-jest): update ts-config configuratin for 6.27 (#318)

This removes warnings about deprecated configuration option:

```text
tsConfig` is depecrated and will be removed in ts-jest 27
```

kulshekhar/ts-jest@8fec681

Thanks!

Author: peterblazejewicz

README.md

@@ -497,7 +497,7 @@ Jest's configuration lives in `jest.config.js`, so let's open it up and add the
 module.exports = {
     globals: {
         'ts-jest': {
-            tsConfigFile: 'tsconfig.json'
+            tsconfigFile: 'tsconfig.json'
         }
     },
     moduleFileExtensions: [

jest.config.js

@@ -1,7 +1,7 @@
 module.exports = {
     globals: {
         "ts-jest": {
-            tsConfig: "tsconfig.json"
+            tsconfig: "tsconfig.json"
         }
     },
     moduleFileExtensions: [