Add a copy of ninja from CIPD to util/bot/DEPS

Interestingly, the Chromium version is a bit behind the default. I've
set it to match the Chromium version.

Bug: chromium:1340825
Change-Id: Ia956e42897add5849dfe09ec8e3a19f704ed9641
Reviewed-on: https://boringssl-review.googlesource.com/c/boringssl/+/55425
Reviewed-by: Adam Langley <agl@google.com>
Commit-Queue: David Benjamin <davidben@google.com>
diff --git a/.gitignore b/.gitignore
index ab8580c..243192c 100644
--- a/.gitignore
+++ b/.gitignore
@@ -21,6 +21,7 @@
 util/bot/libcxxabi
 util/bot/llvm-build
 util/bot/nasm-win32.exe
+util/bot/ninja
 util/bot/perl-win32
 util/bot/perl-win32.zip
 util/bot/sde-linux64