Update ICU to 58.1

source/i18n/plurrule_impl.h

Index: source/i18n/plurrule_impl.h
diff --git a/source/i18n/plurrule_impl.h b/source/i18n/plurrule_impl.h
index 785600bff54cc9d171fcc0dbb7d366613eb6f3cb..c6e4767a096a72c5a7650c05b9d97c437f6d6d7b 100644
--- a/source/i18n/plurrule_impl.h
+++ b/source/i18n/plurrule_impl.h
@@ -1,6 +1,8 @@
+// Copyright (C) 2016 and later: Unicode, Inc. and others.
+// License & terms of use: http://www.unicode.org/copyright.html
 /*
 *******************************************************************************
-* Copyright (C) 2007-2015, International Business Machines Corporation and
+* Copyright (C) 2007-2016, International Business Machines Corporation and
 * others. All Rights Reserved.
 *******************************************************************************
 *
@@ -33,6 +35,7 @@ U_NAMESPACE_BEGIN
 class AndConstraint;
 class RuleChain;
 class DigitInterval;
+class PluralRules;
 class VisibleDigits;
 
 static const UChar DOT             = ((UChar)0x002E);