Fix issue when using redux and checkIntervalOfflineOnly (#133)

### What this PR fixes
If using redux integration and option `checkIntervalOfflineOnly`. 
It will never make a request to check internet connection. 
HOC `withNetworkConnectivity` has internal state, in which connection status is stored.
This however never gets updated. It's only set once during initialisation.

src/withNetworkConnectivity.js

@@ -83,7 +83,13 @@ const withNetworkConnectivity = ({
       }
 
       setupConnectivityCheckInterval(() => {
-        if (this.state.isConnected && checkIntervalOfflineOnly) {
+        const { store } = this.context;
+        let isConnected = this.state.isConnected;
+        // When using redux integration, use store state for connection status
+        if (withRedux && store) {
+          isConnected = store.getState().network.isConnected;
+        }
+        if (isConnected && checkIntervalOfflineOnly) {
           return;
         }
         this.checkInternet();