update_engine: Fix Android.mk typo.

Missing \ was breaking build.

Change-Id: I5f8f3d6dd04d40fb4a909f608ab2524514854998
diff --git a/Android.mk b/Android.mk
index bb76751..9944c15 100644
--- a/Android.mk
+++ b/Android.mk
@@ -52,9 +52,9 @@
         libbrillo \
         libbrillo-dbus \
         libbrillo-http \
-        libbrillo-stream
+        libbrillo-stream \
         libchrome \
-        libchrome-dbus \
+        libchrome-dbus
 endef
 
 # update_metadata-protos (type: static_library)