cmd/bent: restore sparse graphs in tweet-results

The -sparse flag got lost in all the shuffling, and the
tweeted graphs turned into eye-charts.  This restores that.

Change-Id: Id136b848ccaa6cea9e2fb61d9f18c45a8f10c74a
Reviewed-on: https://go-review.googlesource.com/c/benchmarks/+/365717
Trust: David Chase <drchase@google.com>
Run-TryBot: David Chase <drchase@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Michael Pratt <mpratt@google.com>
1 file changed