message: fix(babel): Handle ignored files in babel v7
  * fix(babel): Handle ignored files in babel v7
  In babel v7 `babel-core.transform()` might return null if a file is ignored.
  This makes babel-jest not throw a TypeError in this case.
  * style: Remove trailing spaces
  * Update index.js
diff: @@ -123,7 +123,9 @@ const createTransformer = (options: any) => {
  ]);
  }
  - return babelTransform(src, theseOptions).code;
  + // babel v7 might return null in the case when the file has been ignored.
  + const transformResult = babelTransform(src, theseOptions);
  + return transformResult ? transformResult.code : src;
  },
  };
  };
  