fix(config): support babel config file path as string

docs/user/config/babelConfig.md

@@ -7,7 +7,7 @@ title: Babel Config option
 The option is `babelConfig` and it works pretty much as the `tsConfig` option, except that it is disabled by default. Here is the possible values it can take:
 
 - `false`: the default, disables the use of Babel
-- `true`: enables Babel processing. `ts-jest` will try to find a `.babelrc`, `.babelrc.js` file or a `babel` section in the `package.json` file of your project and use it as the config to pass to `babel-jest` processor.
+- `true`: enables Babel processing. `ts-jest` will try to find a `.babelrc`, `.babelrc.js`, `babel.config.js` file or a `babel` section in the `package.json` file of your project and use it as the config to pass to `babel-jest` processor.
 - `{ ... }`: inline [Babel options](https://babeljs.io/docs/en/next/options). You can also set this to an empty object (`{}`) so that the default Babel config file is not used.
 
 ### Examples
@@ -30,7 +30,7 @@ module.exports = {
 
 </div><div class="col-md-6" markdown="block">
 
-```js
+```json5
 // OR package.json
 {
   // [...]
@@ -63,10 +63,20 @@ module.exports = {
   }
 };
 ```
-
+```js
+// OR jest.config.js with require for babelrc
+module.exports = {
+  // [...]
+  globals: {
+    'ts-jest': {
+      babelConfig: require('./babelrc.test.js'),
+    }
+  }
+};
+```
 </div><div class="col-md-6" markdown="block">
 
-```js
+```json5
 // OR package.json
 {
   // [...]
@@ -105,7 +115,7 @@ module.exports = {
 
 </div><div class="col-md-6" markdown="block">
 
-```js
+```json5
 // OR package.json
 {
   // [...]

e2e/__helpers__/templates.ts

@@ -1,9 +1,10 @@
 export enum PackageSets {
   default = 'default',
   babel7 = 'with-babel-7',
+  babel7StringConfig = 'with-babel-7-string-config',
   typescript2_7 = 'with-typescript-2-7',
   // invalid
   unsupportedVersion = 'with-unsupported-version',
 }
-export const allValidPackageSets = [PackageSets.default, PackageSets.babel7, PackageSets.typescript2_7]
-export const allPackageSetsWithPreset = [PackageSets.default, PackageSets.babel7, PackageSets.typescript2_7]
+export const allValidPackageSets = [PackageSets.default, PackageSets.babel7, PackageSets.babel7StringConfig, PackageSets.typescript2_7]
+export const allPackageSetsWithPreset = [PackageSets.default, PackageSets.babel7, PackageSets.babel7StringConfig, PackageSets.typescript2_7]

e2e/__templates__/with-babel-7-string-config/babel.config.js

@@ -0,0 +1,2 @@
+module.exports = {
+}

e2e/__templates__/with-babel-7-string-config/jest.config.js

@@ -0,0 +1,5 @@
+module.exports = {
+  preset: 'ts-jest',
+  testEnvironment: 'node',
+  globals: { 'ts-jest': { tsConfig: {}, babelConfig: 'babel.config.js' } },
+}