[es6] use correct --harmony-destructuring-assignment flag when preparsing

src/parsing/parser.cc

Index: src/parsing/parser.cc
diff --git a/src/parsing/parser.cc b/src/parsing/parser.cc
index 5d1baf7604122c6a20a1bdbb8d1721f653c26f56..16badca39ea12e76d8525aa5b9cac7a7f73ba7a0 100644
--- a/src/parsing/parser.cc
+++ b/src/parsing/parser.cc
@@ -4924,6 +4924,7 @@ PreParser::PreParseResult Parser::ParseLazyFunctionBodyWithPreParser(
     SET_ALLOW(harmony_sloppy_let);
     SET_ALLOW(harmony_default_parameters);
     SET_ALLOW(harmony_destructuring_bind);
+    SET_ALLOW(harmony_destructuring_assignment);
     SET_ALLOW(strong_mode);
     SET_ALLOW(harmony_do_expressions);
     SET_ALLOW(harmony_function_name);