gitignore: ignore intellij files

BUG=None
TEST=None

Change-Id: I560a1fedb18b95141fd3cd6c794a2eca0e3fe1ba
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/infra/tnull/+/2577195
Tested-by: Sean Abraham <seanabraham@chromium.org>
Auto-Submit: Sean Abraham <seanabraham@chromium.org>
Reviewed-by: Brigit Rossbach <brigitr@google.com>
Commit-Queue: Brigit Rossbach <brigitr@google.com>
1 file changed