Merge pull request #330 from claudiopastorini/master

Start to use ConcurrentHashMap in order to avoid ConcurrentModificationException

Author: minbi

aws-android-sdk-iot/src/main/java/com/amazonaws/mobileconnectors/iot/AWSIotMqttManager.java

@@ -47,7 +47,7 @@
 import java.util.concurrent.ConcurrentHashMap;
 import java.util.LinkedList;
 import java.util.List;
-import java.util.Map;
+import java.util.concurrent.ConcurrentHashMap;
 
 import javax.net.SocketFactory;