Add sourceType as a new mandatory option

Summary:
The `sourceType` option is a new mandatory option for Babel which determines whether to parse the file with the module or script goal. The value "disambiguous" determines this state by parsing.

See https://github.com/babel/babel/pull/7417

Reviewed By: mjesun

Differential Revision: D7685610

fbshipit-source-id: 3958c5ad396592bb1d790e2df4ce315737421a2f

jest/preprocessor.js

@@ -53,6 +53,7 @@ module.exports = {
         platform: '',
         projectRoot: '',
         retainLines: true,
+        sourceType: 'unambiguous', // b7 required. detects module vs script mode
       },
       src,
       plugins: [