Dexlayout: update help string for checksum.

The -u flag to update the dex file checksum was missing from
the dexlayout project help string. No code was changed.

Test: compiles, manual.
Change-Id: I45c1c1a05c58e42c86df1da1ce95cb8cd5f8ce05
diff --git a/dexlayout/dexlayout_main.cc b/dexlayout/dexlayout_main.cc
index 9f73347..c1a3792 100644
--- a/dexlayout/dexlayout_main.cc
+++ b/dexlayout/dexlayout_main.cc
@@ -46,7 +46,7 @@
   LOG(ERROR) << "Copyright (C) 2016 The Android Open Source Project\n";
   LOG(ERROR) << kProgramName
              << ": [-a] [-c] [-d] [-e] [-f] [-h] [-i] [-l layout] [-o outfile] [-p profile]"
-                " [-s] [-t] [-v] [-w directory] dexfile...\n";
+                " [-s] [-t] [-u] [-v] [-w directory] dexfile...\n";
   LOG(ERROR) << " -a : display annotations";
   LOG(ERROR) << " -b : build dex_ir";
   LOG(ERROR) << " -c : verify checksum and exit";