SonarQube issue fix

Author: novalisdenahi

src/test/java/com/configcat/ConfigFetcherTest.java

@@ -524,6 +524,7 @@ public okio.Timeout timeout() {
 
                                         @Override
                                         public void close() {
+                                            throw new UnsupportedOperationException("Not implemented for test");
                                         }
                                     });
                                 }