Upgrade to mksh 50d.

Bug: 17814343
Change-Id: Ie56f48e041850aaf05f44d3640667848ec92f0b1
diff --git a/Android.mk b/Android.mk
index 48a6867..2d572bd 100644
--- a/Android.mk
+++ b/Android.mk
@@ -79,6 +79,6 @@
     -DHAVE_SETGROUPS=1 -DHAVE_STRERROR=1 -DHAVE_STRSIGNAL=0 \
     -DHAVE_STRLCPY=1 -DHAVE_FLOCK_DECL=1 -DHAVE_REVOKE_DECL=1 \
     -DHAVE_SYS_ERRLIST_DECL=0 -DHAVE_SYS_SIGLIST_DECL=1 \
-    -DHAVE_PERSISTENT_HISTORY=0 -DMKSH_BUILD_R=503
+    -DHAVE_PERSISTENT_HISTORY=0 -DMKSH_BUILD_R=504
 
 include $(BUILD_EXECUTABLE)