Update immutable to the latest version: 4.0.0-rc.9

[lwiecek]

Getting this flow error on 4.0.0-rc.2, the error is gone in the latest version, see immutable-js/immutable-js#1379

$ yarn lint && flow && jest --coverage
$ eslint src webpack.config.babel.js --ext .js,.jsx
Error: node_modules/immutable/dist/immutable.js.flow:519
519:   static of<T>(...values: T[]): SetSeq<T>;
       ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ function type. This type is incompatible with
383:   static of<T>(...values: T[]): IndexedSeq<T>;
       ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ function type
  This parameter is incompatible:
    519:   static of<T>(...values: T[]): SetSeq<T>;
                                         ^^^^^^^^^ SetSeq. This type is incompatible with
    383:   static of<T>(...values: T[]): IndexedSeq<T>;
                                         ^^^^^^^^^^^^^ IndexedSeq


Found 1 error