Correctly add googletest's BUILD.gn when updating node.

R=machenbach@chromium.org

Change-Id: I13815463a1bd88d20dbb6f3f656cbda660b77dce
Reviewed-on: https://chromium-review.googlesource.com/979809Reviewed-by: Michael Achenbach <machenbach@chromium.org>
Commit-Queue: Yang Guo <yangguo@chromium.org>
Cr-Commit-Position: refs/heads/master@{#52216}

tools/node/update_node.py

@@ -46,6 +46,7 @@ DELETE_FROM_GITIGNORE = [ "/base",
 # Node.js requires only a single header file from gtest to build V8.
 # Both jinja2 and markupsafe are required to generate part of the inspector.
 ADD_TO_GITIGNORE = [ "/third_party/googletest/*",
+                     "!/third_party/googletest/BUILD.gn",
                      "!/third_party/googletest/src",
                      "/third_party/googletest/src/*",
                      "!/third_party/googletest/src/googletest",