add source map support for better debugging experience (jestjs#3738)

* add source map support for better debugging experience

* Update index.js

* Update package.json

Author: bchenSyd

packages/babel-jest/src/index.js

@@ -67,6 +67,7 @@ const createTransformer = (options: any) => {
     plugins: (options && options.plugins) || [],
     presets: ((options && options.presets) || []).concat([jestPreset]),
     retainLines: true,
+    sourceMaps: 'inline',
   });
   delete options.cacheDirectory;
   delete options.filename;