NaCl: Update revision in DEPS, r13666 -> r13668

This pulls in the following Native Client changes:

r13667: (yyanagisawa) Re-enable use of Goma on Windows, except when using the PNaCl toolchain
r13668: (noelallen) Force rebuild on cmd change.

BUG=none
TEST=browser_tests and nacl_integration
CQ_EXTRA_TRYBOTS=tryserver.chromium.linux:linux_rel_precise32,linux_arm_cross_compile,linux_nacl_sdk_build
TBR=bradnelson@chromium.org

Review URL: https://codereview.chromium.org/513933003

Cr-Commit-Position: refs/heads/master@{#292383}

DEPS

@@ -166,7 +166,7 @@ deps = {
     Var('chromium_git') + '/external/v8.git' + '@' +  Var('v8_revision'),
 
   'src/native_client':
-   Var('chromium_git') + '/native_client/src/native_client.git' + '@' + 'cb44d524fdfeb47a4d5b5946efa439a4f857f080',
+   Var('chromium_git') + '/native_client/src/native_client.git' + '@' + '96f5a229c5ccfcf3725ccc1b4233895bc96588ae',
 
   'src/chrome/test/data/extensions/api_test/permissions/nacl_enabled/bin':
    Var('chromium_git') + '/native_client/src/native_client/tests/prebuilt.git' + '@' + '3e17365176c94624f46cace174f61834b7f3c35d',