Add support for Babel 7 in babel-jest (#3271)

* Add support for Babel 7 in babel-jest

* Fix Flow enforcing string literals on require()

* Update index.js

packages/babel-jest/src/index.js

@@ -19,6 +19,7 @@ const jestPreset = require('babel-preset-jest');
 const path = require('path');
 
 const BABELRC_FILENAME = '.babelrc';
+const BABELRC_JS_FILENAME = '.babelrc.js';
 const THIS_FILE = fs.readFileSync(__filename);
 
 const cache = Object.create(null);
@@ -39,6 +40,12 @@ const getBabelRC = (filename, {useCache}) => {
       cache[directory] = fs.readFileSync(configFilePath, 'utf8');
       break;
     }
+    const configJsFilePath = path.join(directory, BABELRC_JS_FILENAME);
+    if (fs.existsSync(configJsFilePath)) {
+      // $FlowFixMe
+      cache[directory] = JSON.stringify(require(configJsFilePath));
+      break;
+    }
   }
   paths.forEach(directoryPath => {
     cache[directoryPath] = cache[directory];
@@ -91,7 +98,7 @@ const createTransformer = (options: any) => {
         babel = require('babel-core');
       }
 
-      if (!babel.util.canCompile(filename)) {
+      if (babel.util && !babel.util.canCompile(filename)) {
         return src;
       }