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>
diff --git a/cmd/bent/scripts/tweet-results b/cmd/bent/scripts/tweet-results
index dc18851..bee0b34 100755
--- a/cmd/bent/scripts/tweet-results
+++ b/cmd/bent/scripts/tweet-results
@@ -30,7 +30,7 @@
 
 URL="https://perf.golang.org/search?q=bentstamp%3A${RUN}"
 echo ${URL} > ${RUN}.tmp
-(cd bench ; benchseries  -png ../png -series bentstamp -last ns-per-op,build-user-ns-per-op Go*-opt.* !(Go)*-opt.*) >> ${RUN}.tmp
+(cd bench ; benchseries -sparse -png ../png -series bentstamp -last ns-per-op,build-user-ns-per-op Go*-opt.* !(Go)*-opt.*) >> ${RUN}.tmp
 
 wc ${RUN}.tmp
 bench-tweet -i ${RUN}.tmp -m png/ns-per-op.png -m png/build-user-ns-per-op.png -m png/text-bytes.png -m png/total-bytes.png