Add libexpat.so to the grey-list

Bug: http://b/28071598
Change-Id: I5545a06edfd8e0ab5b011392860ddccd6c04677f
diff --git a/linker/linker.cpp b/linker/linker.cpp
index 4478c12..ba5a495 100644
--- a/linker/linker.cpp
+++ b/linker/linker.cpp
@@ -202,6 +202,7 @@
     "libbinder.so",
     "libcrypto.so",
     "libcutils.so",
+    "libexpat.so",
     "libmedia.so",
     "libnativehelper.so",
     "libskia.so",