Fix: Export getRouter() selector

[devrelm]

Fixes #427:

The types file lists getRouter() as being available:

connected-react-router/index.d.ts

Line 68 in f275126

export function getRouter<S extends RouterRootState<LS>, LS = LocationState>(state: S): RouterState<LS>;

It's returned from createSelectors():

connected-react-router/src/selectors.js

Lines 49 to 56 in adc65f8

	return {
	getLocation,
	getAction,
	getRouter,
	getSearch,
	getHash,
	createMatchSelector,
	}

but is not actually exported from the package:

connected-react-router/src/index.js

Line 11 in e444615

export const { getLocation, getAction, getHash, getSearch, createMatchSelector } = /*#__PURE__*/ createSelectors(plainStructure)

connected-react-router/src/immutable.js

Line 11 in e444615

export const { getLocation, getAction, getHash, getSearch, createMatchSelector } = /*#__PURE__*/ createSelectors(immutableStructure)

connected-react-router/src/seamless-immutable.js

Line 11 in e444615

export const { getLocation, getAction, getHash, getSearch, createMatchSelector } = /*#__PURE__*/ createSelectors(immutableStructure)

This PR rectifies this by adding getRouter to the export in each of the 3 files above.

[supasate]

LGTM. Sorry for delayed response.