Fixed goma_ctl.bat to pipe to nul instead of creating a file called null.

Bug: 1066954
Change-Id: Icdf68547f94376616a21997c37cf51cd38659c5a
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/2132954
Reviewed-by: Edward Lesmes <ehmaldonado@chromium.org>
Commit-Queue: Allen Bauer <kylixrd@chromium.org>

goma_ctl.bat

@@ -3,6 +3,6 @@
 :: Use of this source code is governed by a BSD-style license that can be
 :: found in the LICENSE file.
 
-@call "%~dp0\cipd_bin_setup.bat" > null 2>&1
+@call "%~dp0\cipd_bin_setup.bat" > nul 2>&1
 @call vpython.bat %~dp0\.cipd_bin\goma_ctl.py %*
 exit /b