Replace HashMap for ConcurrentHashMap to manage hosts connection states

app/src/main/java/chat/rocket/android/service/RealmBasedConnectivityManager.java

@@ -10,6 +10,7 @@ import java.util.ArrayList;
 import java.util.HashMap;
 import java.util.List;
 import java.util.Map;
+import java.util.concurrent.ConcurrentHashMap;
 import java.util.concurrent.TimeUnit;
 import chat.rocket.android.helper.RxHelper;
 import chat.rocket.android.log.RCLog;
@@ -25,7 +26,7 @@ import rx.subjects.PublishSubject;
  */
 /*package*/ class RealmBasedConnectivityManager
     implements ConnectivityManagerApi, ConnectivityManagerInternal {
-  private final HashMap<String, Integer> serverConnectivityList = new HashMap<>();
+  private final ConcurrentHashMap<String, Integer> serverConnectivityList = new ConcurrentHashMap<>();
   private final PublishSubject<ServerConnectivity> connectivitySubject = PublishSubject.create();
   private Context appContext;
   private final ServiceConnection serviceConnection = new ServiceConnection() {