[redux-mock-store] Update types to be compatible with redux 4.0

[chungnho]

• Use a meaningful title for the pull request. Include the name of the package modified.
• Test the change in your own code. (Compile and run.)
• Add or edit tests to reflect the change. (Run with npm test.)
• Follow the advice from the readme.
• Avoid common mistakes.
• Run npm run lint package-name (or tsc if no tslint.json is present).

If changing an existing definition:

• Provide a URL to documentation or source code which provides context for the suggested changes:
  • redux Dispatch now takes an Action as a generic instead of the State
    • https://github.com/reduxjs/redux/blob/v4.0.0/index.d.ts#L115
  • The redux StoreCreator now adds Store Extensions from StoreEnhancer to the return type
    • https://github.com/reduxjs/redux/blob/v4.0.0/index.d.ts#L222
    • reduxjs/redux@cbdca62#diff-b52768974e6bc0faccb7d4b75b162c99R222
  • In particular, when applying middleware, any Dispatch signature added by the middleware is in turn added as a Store Extension via the StoreEnhancer.
    • https://github.com/reduxjs/redux/blob/v4.0.0/index.d.ts#L327
    • https://github.com/reduxjs/redux/blob/v4.0.0/index.d.ts#L277
  • Since createMockStore takes an array of middleware instead of the more complex way that redux createStore does it , it's not possible/easy to programmatically figure out what extra Dispatch signatures are added by the list of middleware. Adding the DispatchExts optional generic allows one to manually ensure that any extra Dispatch signatures for their middleware can be added.
• Increase the version number in the header if appropriate.
• If you are making substantial changes, consider adding a tslint.json containing { "extends": "dtslint/dt.json" }.

[typescript-bot]

@chungnho Thank you for submitting this PR!

Because this is a new definition, a DefinitelyTyped maintainer will be reviewing this PR in the next few days once the Travis CI build passes.

In the meantime, if the build fails or a merge conflict occurs, I'll let you know. Have a nice day!