Make sure ActionCreators will work with es6 arrow syntax

[therealcisse]

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In some es6 transpilers, ES6 arrow functions are bound to the current scope making it impossible to call this.dispatch(...) or other methods of the ActionCreators inside the callback.

By passing context as the last argument to the ActionCreator, one can use context.dispatch(...) or other methods of the ActionCreator.

Since context is passed as the last argument, all existing code work as is and if you don't use es6 arrow syntax, you're not affected.