add gcov file extensions (.gcda and .gcno) to .gitignore

BUG=none
TEST=gcov files no longer appear in git status

Change-Id: I455e6445e32a6fdef2cb381b994908a17bde3e0f
Reviewed-on: https://gerrit.chromium.org/gerrit/45142
Reviewed-by: Duncan Laurie <dlaurie@chromium.org>
Commit-Queue: David Hendricks <dhendrix@chromium.org>
Tested-by: David Hendricks <dhendrix@chromium.org>
1 file changed