Fix unit test failing with ConcurrentModificationException; during close

all, take a copy of the list of loggers for iteration

Author: pxcurtis

src/main/java/org/fluentd/logger/FluentLoggerFactory.java

@@ -19,6 +19,7 @@
 
 import java.lang.reflect.Constructor;
 import java.lang.reflect.InvocationTargetException;
+import java.util.ArrayList;
 import java.util.Iterator;
 import java.util.Map;
 import java.util.Map.Entry;
@@ -112,7 +113,7 @@ Map<FluentLogger, String> getLoggers() {
     }
 
     public synchronized void closeAll() {
-        for (FluentLogger logger : loggers.keySet()) {
+        for (FluentLogger logger : new ArrayList<FluentLogger>(loggers.keySet())) {
             logger.close();
         }
         loggers.clear();