_content/doc: fix errant '-' in telemetry.md

This is a grammar rules that my fingers will never learn, and sometimes
my eyes do not notice...

Change-Id: If6c5e8b45702844996f13802ffb041d0e7d6a322
Reviewed-on: https://go-review.googlesource.com/c/website/+/598696
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Hyang-Ah Hana Kim <hyangah@gmail.com>

_content/doc/telemetry.md

@@ -62,7 +62,7 @@ This page explains how Go telemetry works, in some detail. For quick answers to
 frequently asked questions, see the [FAQ](#faq).
 
 <div class="DocInfo">
-To <strong>opt-in</strong> to uploading telemetry data to the Go team, run:
+To <strong>opt in</strong> to uploading telemetry data to the Go team, run:
 <pre>
 go run golang.org/x/telemetry/cmd/gotelemetry@latest on
 </pre>